My guess would be they really aren't a good solution because:
1. AL tanks have flat bottoms and don't really need boots in the first place.
2. I've always been foot-heavy in A80s to begin with (since they're so long), having a permanent weight boot exacerbates this, and also limits options for managing trim by moving weights around.
It could be great for ladies and others with floaty feet. Well maybe not great.....