What aspect of trust bothers you? Sudden failure? Suddenly going into some wild behaviour? Before I tried one they appeared like something fraught with possible ways to do bad things. Having played with one I only see one potential really nasty thing which could happen....
The ones I have tried are very easy to get started with, unless you behave in a very cavalier manner. You need to get used to wiggling your foot in the right way, to get the response you need from the machine. That took me about 5 minutes of working with one foot on the machine, and having it move in fairly wild (although not very dangerous) ways. Once I had that skill sorted out, putting the other foot on the machine and balancing there was trivial. I don't see much potential for any serious injuries during this learning stage, as long as you show reasonable caution.
My next issue was what could happen in the event of a massive power failure, while you are travelling at speed. If you ignore the low battery warnings you do actually get to the point where the power is suddenly cut. However, the machine's maximum speed is such that you can step off under such abrupt circumstances, and slow yourself to a halt over a few paces. Again, it seems hard to get yourself into serious trouble if you are moderately cautious.
My next issue was what could happen if the control systems go wild. This is the one area where I suspect you could get into serious trouble. When you want to spin in a circle, these machines can do so quite fast. If that happened due to a failure, rather than under your control, I suspect you would have a fairly powerful machine thrashing at your feet, with real difficulty getting yourself clear of it. That possibility does concern me.