Most of the negative reviews/critiques that I've read are really complaints about MINI-bikes in general...NOT the Magnetrainer. So before you read any more brand reviews (including mine), do yourself a favor and think about your expectations for a moment.
1. Are you looking for something that provides a low-key, no-fuss, no-muss way of adding extra activity to your day (maybe at work or something casual while you knit)? Are you looking for something to conveniently rehab with? Are you cramped for space, and able/willing to accept that MINI-bikes have more limitations (due to simple physics) than standard-sized bikes?
*** If you answered YES to these, then skip #2 and #3, because you've got realistic expectations about MINI-bikes, and you'll want to know why the Magnetrainer is a brilliant way to go. ***
2. Are you looking for the same level of difficulty as a marathon spin class at your local gym?
*** If YES, then a MINI-bike isn't for you. ***
3. Are you able/willing to accept that the physics of MINI-bikes requires certain compromises?
*** If NO, then a MINI-bike isn't for you. ***
Now, for those who've decided that a MINI-bike fits their bill...let's talk about the Magnetrainer. First of all, the quality is exceptional. The frame is sturdy and well-designed. The pedaling motion is extremely smooth and quiet. The bike comes with simple, clear instructions and it doesn't take much time to assemble.
Stability issues are minimized by the Magnetrainer's weightiness and the width of its base. Additionally, you can extend the front base and use the velcro strap to tie the bike to your chair.
You may need to make additional modifications if you're doing some very strenuous peddling, but that's the nature of MINI-bikes, since there's not as much weight holding them down (less bike weight and none of your sitting weight). Maybe use a higher chair so your legs are more vertical and/or invest in a rubber mat. Another option is to find a way to secure the base to the floor.
For those looking to peddle while at a desk: unless you have about 3 feet of clearance (+ or - a few inches), you will need to push out your chair to keep from hitting your knees. Once again, this is just the physics of MINI-bikes, and something to consider before you decide to buy one. In order to stay productive while peddling at work, I purchased a height-adjustable laptop cart/laptop caddy. (You can find one at WalMart for $39.)
Contrary to one complaint I read...the Magnetrainer has an exceptional tension range. All but the most dedicated cyclists/spinners will find the intensity more than adequate. Remember, MINI-bikes don't sell themselves as an equivalent substitute for $800+ equipment. Convenience and portability is the main selling-point for MINI-bikes, and these features involve a tradeoff. Based on my experience, you compromise the LEAST with this brand. If the Magnetrainer doesn't work for you...no MINI-bike will.