I saw this post before but didn't have time to reply. Just got off mine so while it's on my mind, will do a quick reply.
I've been using a nordic track for years & about a year ago decided I needed to try to target a different set of muscles to add to my weekly workouts, alternating w/ the nordic track. Was looking for a rowing machine but the salesman talked me into the health rider. I've been pleased w/ it but I only use it in one way. I know there are numerous positions, etc., but from what I understand, most will just use the same muscles I'm already using w/ my nordic track. So in your case, if you're not using any other machines, I'd suggest you learn to use all variations so you're using most muscle groups. The one I use is w/ my heels mostly on the pedals, w/ my toes pointed out, w/ my hands on the middle bar, so I'm targeting my abs & thighs, mostly inner thighs. I've put all the weights on the seat bar plus I wear a 20 lb vest, but I've been exercising & maintaining for years so I wouldn't recommend that for a beginner. I found the bars rubbed my hands so I wear those fingerless weight gloves. My understanding too is that you really need to pay attention to your posture so it doesn't hurt your back. I use it for 30 minutes. I really feel my muscles being worked so I think it's a good machine. The main drawback to this machine, as w/ any nonmotorized machine, is you need to push yourself - as you get better at it, make sure you make yourself either add some weight &/or push a little harder &/or faster.
enjoy!!