Big fan of Steel It here. Used it on my C10 build and, apart from the prep time, really like it. Very durable, good coverage and it is indeed weld through. Expensive but worth it.
Think I'll use it for a bumper I just had mad. There's some spots later on I may modify or grind, so knowing I won't completely blow the finish, and it'll be protected until then seems worth $30
If you sprayed multiple coats over and over after letting it dry in between, would a lot of weight be added to the object? Or is this spray lightweight
Good question. I would think Steel-It is going to be slightly heavier than an oil-based enamel paint just because it does contain a metal flake, but I think you would have to put on a ton of coats before you started to notice any added weight as compared to your typical rattle can paint. Probably a good question for the manufacturer?