1. There is no reliable fix for the 20mph max for the x35. An Australian firm has had mixed results that you can research on this website.
2. I don’t use a heart rate monitor but others report good results if compatible
3. I would say the Nyrto out performs the Dyodo and producing two race type bikes is not a good business decision.
4. The performance of the x35 fits my needs, helps going up the hills and it’s easier to hang with my riding group. I’m the oldest in my group at 73 with bad knees and have been biking for 38 years. Other folks may have different needs. If I had a do over, I would make the same purchase.