yeah, I think FlexSeal could only be used as a "topcoat" for grip. I've used FlexSeal to spray the bottom and bottom 1/2" of my steel water bottles (Sigg) and it works great. Even used it to seal a hole in the bottom edge of one of them after it got dropped. I sprayed on a few layers to make it a little thicker to protect the bottom/edge, as I drop them frequently ... ... and it really does absorb the impact now, quite well. If dented, can use a rubber mallet to reshape the bottom.
Guess I could do the commercial for them now, but it's handy stuff!