With minimal research it seems that JB Weld is epoxy resin and cures to be hard and unyielding. Sugru seems to cure to a silicone finish, and hence is firm but yielding. Sugru also appears to be more adhesive - JB Weld has to be moulded around something to make it adhere.

Its properties are here : http://sugru.com/about/ : and even to my first glance it seems completely different from JB Weld. Did you bother to look at the web site before asking your question?