Blasto Wellsi reproduce by growing little babies next to the larger polyps. They have their own hard round coral skeleton and over time, which is a long time, will grow larger. Blasto Merleti grow much faster and grow a hard skeleton right next to the main colony and a new polyps comes out of it. Kind of like a honey comb type of think.
Some people have cut a larger polyp away, on the Blasto Wellsi, and single babies start to grow right away.
I wouldn't recommanding cutting away any of the polyps, unless they're seperate already and there are no other polyps around it, as you can easily damage and probably kill the other polyps.
There really isn't any comparison as Merleti grows very fast, well not as fast as zoo's, and Wellsi is very slow and most of the time for every new baby or two you may lose a large polyp. The cultures Wellsi that you'll see usally have very small polyps as compared to the wild ones. Merleti is usally availble as frags, last frag swap I sold some.