listen, I'll be 40 this year... I've done a triathlon, bicycle centurys (100 mile), Karate tournaments, and got a 295 out of 300 on the US Army Physical Fitness test (running was never my thing)
I've done soloflex, bowflex, nautilus, you name it...
not to say their bad, but nobody has won anything by training with only them, if that's all you got, go for it.