JB-Weld is my go-to product, I'd be lost without it.
I can see that Lab Metal might be problematic in some situations. JB-Weld is a 2-part epoxy, it hardens once it's mixed, air or no air.
Can Lab-metal be used to join two items?
No. Lab-metal is not intended to be used as an adhesive. Because it hardens by exposure to air, it will not dry when "sandwiched" between two parts.