I like to be able to see if things are wearing out rather than have a 'black box' system which is either working or broken, and when bits do wear out I like to be able to choose what I buy to replace them.
This is key for me. I had one for 2.5 yrs with no problems and wondered if it was actually the Holy Grail. It failed on me at the start of a holiday and the lack of parts/expertise meant it had to be abandoned (the hub, not the holiday thankfully). With a conventional system you can always bodge it somehow and parts are readily available.

