Re: engine and rear hub
Of course it's a good deal!
...all the china stuff is a good deal for the money !!!
I have not run one of the kits you pictured. As with the rest of the china stuff, quality is probably lacking.
IMO, a Worksman or Husky wheel is probably better and a disk brake is the way to go when you discover your speed will nearly always be in excess of normal pedal speed, (unless you are Lance Armstrong).