yeah, i think the dedicated namebrand stuff is better. but it's hard to know what suits your needs cos you may only need the lesser benefit of Flashtac, whereas g-spot/dynamat/etc may be overkill.
...although it's hard to go 'overkill' with SDer; you usually never have enough. :roll:
i've used Flashtac in some places in my car and it works well there (had no probs with it falling off either, but it's not in/on my doors or exposed to the elements; it's in my boot). but admittedly, i've used dynamat xtreme in the more important spots like my doors and find this stuff excellent.
so, 'some' is better than none, and if you're on a really tight budget, consider Flashtac. otherwise, if you can afford it, consider other products.