All depends what you want it for.
I have that kit and yeah, it's fast (and dangerous) on a bicycle - mine is a hardtail Specialised Rockhopper, Rockshocks Toras on front (vintage!).
My thoughts are:
1) Great if you have no chance of rear punctures i.e. live in Essex. Nightmare if you think you're going to be off road with any stones at all. Think Wales, Scotland, Dartmoor, etc. Definitely need serious back tyre for that like Schwalbe Eddy Current (£70?) and rimwhateveritis. Good luck with rear punctures.
2) Not as easy to fit as made out. I got the 9-speed and wish I hadn't, get the 7-speed if you must.
3) You really do need to be competent at DIY, have a shed, tools, skills, etc.
4) Couldn't agree more with Nealh "An already legal moped would make more sense." Sooooo much easier. I'm used to motorcycles, plus, if you bin a bicycle/mtb at 30mph without proper gear it will go badly.
Better still, get a Yamaha YZ125cc (or WR450cc if you're brave) and see what you think. I really still don't get all this EMTB stuff. I guess it's for folks that haven't ridden motorcycles or like myself, are old and trying to recover from injury/illness.
Re reliability:
All good so far! (60miles). Apart from the disc caliper still rubbing on the hub, just. The caliper has been ground off both sides, adjusted, adjusted, adjusted... Rear stays had to be jacked out to fit the wheel/hub, etc, etc.
Don't have the controller in a bag, it gets proper hot! As Dudestuff says, fit on the battery or anywhere but obv waterproof as much as poss, definitely needs airflow.
No screen problems/battery yet.
So, brilliant then. I'm trying Bafang on a FS next.