I rode a bike just like that a few months ago. Very basic level components, obviously nothing fancy or too durable at that price point. Personally, I wouldn't get a 24v system as it is going to be pretty slow. Top speed of 15mph, so if your OK with that, what the heck. I am building a 36v kit with what looks to be the same parts, and the kit cost $500. So, for an extra $300 you are getting a bicycle and installation. Not too bad of a deal I guess.
If you really got bored some day, you could put in a 36v battery into that system and be good for 20mph.
I would put the speed at 14-15mph, and the range at 20 miles (not the 27 they list) but that of course all depends on how much you pedal.