Well a "sleeve" type coilover is just that. It's a spring mounted on a perch that are dual locking nuts that are on this "sleeve" that is mounted on the shock. It's held on there by either grommets or allen screws. Not really something I'd trust but it seems to do the job. These are most suited for universal applications so almost any car can have height adjusting coilovers.

A "true" coilover is an all inclusive unit where the threading is already on the shock. The spring still sits on dual locking nuts, but the spring rates coincides with the dampening of the shock. Plus most of the time, the spring is a progressive wound spring and usually includes upper pillow mounts. These are application specific so they would be most beneficial for the car that it's going into.

In terms of being the same. If you just need something that can raise and lower your car, you're better off with the GC's and a good set of aftermarket shocks (to prevent bottoming out). It's easier on the wallet which in turn could help you buy other beneficial suspension parts (like bars and bushings and whatnot).