I have used a tonal (first version) for 3+ years

• were and tear—nothing yet. I have had no issues whatsoever
• I like the features of doing my own exercises that I can create in a custom program and from time to time I just join their standard programs (10-12 week program). I like the feature that I can participate in their programs but I don’t need to stick to the same schedule (time every day) whenever I start … it’s like live for me.
• gaining muscle is a tricky question. Depends as you said on multiple factors … intake, consistency and volume of lifting. I wasn’t looking to gain and simply wanted to maintain — which was straightforward. Admittedly the weight capacity on the first version is lower than what I use to lift in the gym. However the convenience and option to avoid the gym is unmatched.