Rowing machines are good for all round fitness, but correct technique is non-intuitive and takes a long time to learn. Done correctly it will build core strength, legs and shoulders. But most importantly cardiovascular fitness. It is low impact so it should be fine on your knees as long as you aren’t splaying your legs apart on the drive. I would personally recommend an exercise bike / spin bike in place of a cheap rowing machine for cardio especially if you can’t be bothered with the technical aspects. Just sit on the bike, watch tv, get your heart rate above 130bpm for an hour, easy peasy.
I think I went Ubuntu > Xubuntu > Mint > Lubuntu > Kubuntu > Arch (LXQt) > Arch (DWM)
Mint was great as a relatively new linux user. LXQt is fantastic on old hardware. After KDE I really wanted to try a tiling window manager, really enjoying it so far.