I haven't tried either, but from what I've read, InstaMorph (aka "Friendly Plastic") needs heat to melt it and make it moldable, and can be reused indefinitely simply by re-melting it.

Sugru, on the other hand, does not need to be heated. It is moldable immediately after opening the package, and it self-cures at room temperature 30 minutes after being opened. Once it cures, it can not be reused.

From what I've read about it, Sugru sounds very much like ordinary epoxy putty, except that it might be softer or more rubbery than regular epoxy putty once it's cured. Or maybe it could be called a silicone in an epoxy putty-like form. While "Friendly Plastic" is more like ordinary plastic that's moldable when very warm.