I went looking specifically for the Bionix conversion kit and the local bike retailer said that in his view the company and the technology weren't there yet. The technology kept breaking down and the company wasn't responsive so he stopped carrying the produce line.

This is just one datapoint so it would be good to hear from people with good experiences of the conversion kit.

I go riding once a week with someone who's had a Bionix conversion for just a few months. So far it's not been a problem (except for me keeping up on the hills), other than for an initial issue caused by a loose connector. It's heavy though, and I wouldn't want to pedal one unassisted for long.