The Bionx kits have an internal strain gauge that continuously monitors how hard you pedal. It provides the smoothest, most silent and organic-feeling pedelec boost on the market. Once you get going, there is no surge or delay in turning on or off, creating the intoxicating feeling that there is no motor involved- you just inherited superman's legs!
Range is excellent on the lower assist levels, with matched, proprietary battery packs and safe lithium cobalt technology. The battery and motor unit communicate with each other, and aftermarket packs are not an option, although there is at least one vendor who rebuilds the Bionx packs. This makes for a less expensive option when your pack wears out.
Bafang-based hub drive kits do not offer nearly as good a pedelec experience. Sensing is crude and laggy, gearing is noisy, and most users rely on throttle control. As good or better than Bionx if you just want effortless no-pedal power, but poor if you want a seamless electric pedal assist that seems to disappear into the background.
Battery packs are completely up to the user, allowing more scope for customizing range VS power and cost. However, it's also buyer beware, with lots of questionable choices out there.
Bionx are also as close to zero maintenance as you can get- designed and built in Canada, water sealing is excellent, the hub drive has no internal gears to strip or need replacement, and doesn't stress the drive chain. The warranty is longer than Bafang.
In contrast, the Bafang-based drives (mid or hub drive) all have internal plastic idler gears that are a weak link, problems with drawing water into the electronics, and a history of controller failures. Maintenance and repair issues are commonly reported on the forums.
The latest mid-drive Bafang versions seem to be better developed, but they place tremendous stress on the derailleur and chain, twice as much or more than human power alone. Expect to blow chains and other driveline parts regularly if you ride aggressively.
However, Bionx kits are very expensive- at least twice the price of any Bafang-based product. Tech support is excellent in North America and Europe, but I don't know about India. Best if you want a sealed, no-fuss experience.
Bafang kits are much more affordable, have a strong DIY community on various forums, and there are more sources for replacement parts when they break. Best if you want to experiment, tinker, and especially if you want to hot-rod your kit for more power.
