I have the same kit (I think) and have run it for 3 years now. It is a decent, reliable power assist that works pretty well out of the box. I changed connectors and got a new, better quality charger. Also the batteries seem to last one summer, I am on my third pack, they are about $100US a set for lead acid. My kit is a 36V, 600W brushed hubmotor from Wilderness Energy.
I have not had problems with the bolts loosening up and axle spinning. I use a suspension fork with no problems but I have a high quality ($) bike not a mart of wal special (Giant Sedona).
The most important thing is to properly mount your batteries. I have a rear rack, a battery bag and straps for each battery. It still jumps around a lot. The best would be a battery box mounted inside the diamond. Either way it has to be sturdy and tight.
It is great for short trips in town. It is not extremely fast, at 18mph, but is great in downtown traffic. Basically you are pedaling and you can get a boost when you need it up hills, crossing streets, etc. Plus when the charge is fresh you can move pretty fast on a straight away (18mph). Its better than pedaling.
The down side is that the range is only 10 to 12 miles, which means you can only ride for a half hour, more or less. Thats just not enough. Then you wait for 6 to 8 hours while it charges.
The best way to ride it is to pedal like a bike and use the power only when needed, on hills, starting up, etc. If you conserve, you can go quite a bit further than when you just power everywhere and don't pedal.