I was pleasantly surprised with the quality and usability of this phone. The specs are pretty darn good, other than it's modest half-gig of RAM. It is quite responsive, and the screen is pretty good as well. The faults are noticeable, but certainly not deal breakers. If you are looking for a good, new, unlocked Android smartphone for under $100, this is a great option. I am using it with PureTalk GSM (ATT network), on a $10/month voice and text plan, and this has worked great.

Pros:
Thin and sleek
Fast processor
Fine call quality
Good external speaker
Nice big screen
Responsive UI
Good WiFi and cell reception
Dual SIM
Includes screen protector
Good battery life.
LESS THAN $100!!!!

Cons:
Limited screen viewing angle
Limited RAM
Not HD/Retina resolution
No auto-brightness
No port covers (allows dust etc. into the phone)

Tips:
There a couple things that you can do to ensure that this phone performs well despite it's shortcomings. First, in developer options change "Window Animation Scale" and "Transition Animation Scale" from 1x to .5x. This will allow the UI to scroll smoothly and remain more responsive even when background apps are running. Turn on "Force GPU Rendering" in developer options as well to help with this. Because of the limited RAM it may also be beneficial to get an App Cache cleaner, and limit the number of things allowed to run in the background in the developer options.

Update: 10/26/14
8 days after I received this phone, and 2 days after I reviewed it, it failed on me. The screen started flashing scrambled colored lines, and became unusable. This happened without warning, and was not due to dropping, bending, flexing, squishing, hitting, or damaging the phone in any way. The phone has been in an ArmorFlex case, and had a screen protector on it since I unboxed it. There appears to be a spec under the glass, so the only thing I can think of is that a dust or sand particle got inside the phone and sandwiched between the glass and the LCD screen itself causing damage to the delicate LCD. I work an office job, and have not been out doing anything in extremely dirty environments with my phone, so I am pretty annoyed that this happened. I am leaving my review at 4 stars, as I still think this phone is a great deal, but may change that if my replacement fails. The replacement should arrive today, and I have already ordered rubber plugs for the USB and headphone ports to prevent anything from working its way inside the new phone.
So, lets add one more con to the list.

I bought this phone, and was excited when I opened it. It came with everything, including the earphones, case etc. I was surprised by the size of the phone, which I also liked because my old phone had a screen display of 4.5". Another thing about the screen, its not a high resolution, so would recommend the phone with hd display. But other than that, the screen is fine too me, everything looks nice on large screen. The camera is also great too, and video records good too.

So I have spent a few days with this phone now. My verdict It's not a bad device, Mind you for around $100, its not that bad.The local phone shops are selling these phones for twice this.
I do have a few grips though.

So my first complaint is the screen yeah it's pretty bad.
Resolution aside, knowing I was getting a lower resolution device (basically 480P kind of resolution) I wasn't too upset with that, but yeah it's bad.
The viewing angle is where the issue is, if you're not looking at it dead on, the image looks like the typical "old school"
LCD, where the colors are inverted, but the image quality even dead on is kind of washed out,
but the touch screen is really where this phone wins no love with me. It seems as if the sensitivity could have been tweaked
a little, but there is no way to adjust that in the menus. Also, again with the angle of view if you are trying to complete an action
with the touch screen, and the viewing angle is not dead on, then you're not activating the proper buttons on screen and that damned back button! Sometimes it just wont work

This complaint is a short one, but it's the front camera, the resolution is horrible, especially if the light is indoor.

I also have to report that the sound through the earphone jack is not great, there is just no bass, I have heard equal sound
quality from those cheap radios they give away for contests, and such.

My last complaint is really not an issue that most users will even care about, but this phone is near impossible to root, considering this phone I'm sure is not on anyone's favorites list, and therefore development on this phone is practically non existant

Pros:
Low cost solution for an immediate replacement
Decent battery life has pretty good standby life
Runs Kit Kat A lot of name brand manufactures are still stuck on Jellybean, or older
Dual SIM Can have basically two phones in one
5" screen A lot of name brand manufactures seem to charge a premium for screen size
No bloatware A lot of name brand phones come with a ton of bloatware that you just can't remove

Cons: Look above

Overall I'd say that this phone was definitely worth $100, especially if you (like me) break your phone, and need a cheap replacement, but with the things that I have listed above that are an issue with me, I have been considering buying the $150 Studio 5.0 C HD, or better, and just shove this phone in a drawer as a backup. Coming from phones manufactured by the likes of
HTC, Motorola, Samsung, and so on, I'd have to say that this company BLU is impressive with their line up of phones, they pretty much have a phone that will suit anyone at a fraction of the cost of the other guys

I personally think is a Very good phone! Im a nursing student and anyone whos in nursing school knows that our lifes consist of reading books and family time . no time to be able to work full time. I closed my contract with sprint and decided to go "prepaid" and i love it. The phone was cheap and the plan i chose is cheap as well. Im with the Walmart Family Plan and text/calls are unlimited for $24 a month. No contracts, Pretty good deal until i graduate. or i would keep it and add data. I still have internet around the house and at school so i dont really need "data" since now days there's WIFI literally everywhere :)

I RECOMMEND you getting this phone if youre looking for something cheap ! I read reviews everytime before i buy anything and this is the whole reason im writing this. its worth it !

This work great for me then the LG 9 phone I had. Like feature on the BLU 5.0 Studio hd phone work well w/ T-Mobile sim card and the pay as u go plan. Had a lot of friends thinking about getting one. Price and quality for this is phone glad got it. But I wish BLU would have more variety cases for this BLU Studio 5.0 HD phone.

i ordered this from walmart in case i had to return it i could just go to the store in my town. the phone is better than i expected especially for 87$ i got the yellow one. its more of a lime color. huge screen. 5inches.. came with a clear jelly case, charger with detachable usb cable. and head phones. i had to buy an sd memory card. and i use a straight talk sim..it has a front & back camera with panorama view. only had it 2 days, so far so good! the packaging was neat too. the lighter is for reference of size and color.