Hail protection nets are a COTS product. Full stop. Properly-designed nets are exceptionally strong; that's why we make "bulletproof" vests out of them (that's all they are, just a fiber net with a very tight weave).

Just because your local car dealership(s) didn't opt for hail protection nets isn't on its own evidence for or against their effectiveness. There are a great many factors that go into such a decision and, unless you were privy to the decisionmaking process itself, whether or not nets were considered -- much less their effectiveness -- is pure speculation on your part.