Actually, the Spinervals I have show riders on spinning bikes (with resistance settings) and bikes with trainers. Coach Troy will tell you the resistance setting to turn the knob to AND he will tell which chainring (front) and gear (behind) to use, so yes, they are geared to both spin bikes and regular bikes on trainers.
If he tells you a certain resistance and you can't finish the exercise or set at that resistance, definitely back down. You'll get a feel for what you can do. He's big into the cadence (or tempo of pedaling). On some exercises, he will have you pedaling at a cadence of at least 90 rpm's, sometimes way up over 100 rpm's. That's pretty fast. If you can't pedal that fast, then definitely go for less resistance to keep the cadence up.
Hope this helps.
Jeanette