I was in the market for the best way to add air to my tires from an air compressor, but also to monitor the pressure easily while doing so. This unit seemed to fit the bill... just attach it to take the reading and then top it off if needed using a cheap air chuck. I also liked that it has a relief valve. So you can get your pressure perfect without taking things on and off the valve stem.
The gauage reads quickly and seems to be accurate. It is relatively easy enough to pop the chuck on and add air. It can be a little cumbersome trying to hold it while pusing the chuck on, because the chuck needs a bit of force to engage (also depends on the pressure you have your system set at). Overall, there are some ergonomic drawbacks. First, you can only hold it in your left hand if you want to add air and see the gauge, which is OK for me, but maybe not for some. The round shape is alright, but you have to hold it in a very specific way to brace against the pressure needed to engage the air chuck to add air, and it's not always the most comfortable or convenient position. My air chuck has the angle as most do, so I have to press it in with the air hose sort of sticking out at me, which is harder than if I had a straight air chuck (I'll have to see if they make one). This may be a problem with my air chuck, but since most are angled this way, it would be easier if this unit were easier to get a good grip on, or if it had more room between the gauge and the air chuck input. Something like a pistol grip handle on the bottom of the gauge and an inch extension on the air input would be awesome. I don't want to get into a long list of ergonomic suggestions... suffice to say that the ergonomics are definitely not perfect, in my mind.
I do like the way it connects with the quick release lever. No need to spin anything on, or push and activate a clamp (ie like a bicycle pump). The one problem with the quick release lever is that it seems that it's 50/50 whether or not you get a good seal. Half the time you push the lever, slide it onto the valve stem as far as it will go, let go and it seals, half the time it does not seal and leaks. I found that the tip here to stop it from leaking, is to, once it is locked on (but leaking), turn it onto the valve stem a little in the clockwise direction (tightening). This will seal it up just fine. The best I can tell as to why this happens, is that it looks like the locking mechanism (the part that holds it on the stem) is threaded to match the thread of the valve stem. Sometimes it grabs the threads and locks before it bottoms out and seals, and without rotating it a little (in the clockwise tightening direction), it just can't bottom out and seal. Because of the helical nature of the threads, with this type of design, it really can only be 50/50 whether or not it seals (unless it had a thick cushy o ring that could compress enough, but then I guess you could risk not having a tight enough seal for certain pressures). So, this seems to be why half the time you must turn and tighten it a quarter turn or so for it to seal on the valve stem. It's not too big of a deal, but it would be a lot nicer if it just sealed right the first time without any fuss. If it's not possible to have a quick release setup that perfectly seals (and it might not be, I dunno), then I suppose that even with this problem, it's still quicker and easier than the other methods I've seen of the bicycle pump foldover clamp type, and the spin on brass coupler type.
The last problem is that the item feels cheaply made. From the locking mechanism not locking solidly to the rubber grip on the gauage just being a cheap rubber cover (like a rubber cell phone cover) that twists and contorts every time you hold it (instead of being molded right to the gauage), it just does not feel like it will last. Only time will tell, but it's my opinion that, overall, it is not a high quality piece that will last. The rubber cover is the most annoying part, because when you're trying to add air and need a good grip, it just flexes, stretches, and squishes all over. I might try to just take it right off.
Overall, I think this is a convenient product that I will use until it dies. I'm really not sure there is a better product out there? I looked at the unit that is gauage/air chuck in one with the rubber hose, but it was pretty expensive at roughly twice what this unit + an air chuck costs, and didn't have the relief valve. This setup looked like it would be better overall. I have used the other type unit before, and I will say that I do like this setup better, but would prefer it had a little better ergonomics and build quality.
I would buy it again, but before I did, I would double check to see if there is a product out there that performs the same function, but is of higher quality and perhaps improved ergonomics. I would pay more for that product, if it existed. If not, this thing beats the heck out of adding air with a chuck and then using a separate gauge to check the pressure, and repeating. So, not perfect, but definitely a good and convenient product.
Hope this helps!
!!UPDATE!! -- 08-26-11 --
I've owned and used this tire gauge / filler for about 4 months. If you read my original review, you'll notice that I thought it was cheaply made and had ergonomic issues. I originally gave it 4 stars, but after using it even more, I kind of wish I only gave it 3. It's just too cumbersome to use when you're trying to add air with a chuck.
What's worse, is that the valve stem where you add air starting leaking air every time it was connected to a tire. I could hold my finger on the stem just so, and it would stop/slow the leaking so I could get a reading, but it was still a PITA. I suspect I could just buy a (or find my) valve stem tool to tighten the stem in there to prevent this, but after 4 months and being used maybe 4 times, I don't think this should have happened. I'm reducing the stars to 3, but not really because of this problem, as I mentioned earlier in this update, this thing got more and more on my nerves as time went on anyway, even without the leaking.
Instead of tinkering with this unit and trying to fix it, I've retired it and replaced it with a digital tire inflating gun. I don't want to get into a full review of that unit here, but if any of you are looking for the perfect way to inflate tires, that's it. It's a bit expensive, but it's solidly built, warranted forever, ridiculously easy to use, ergonomic, the quick release seals very well without tinkering, the list goes on. Something I'll be using for years to come. Instead of saying "ehhh I don't want to go to the trouble of topping off or checking the air pressure because I don't want to struggle with my inflator setup", now I look forward to it because it's so easy and fun. It's everything I wish this unit was. If any of you are looking for a better way, you can investigate the griot's garage tire inflating gun.