Hydros are illegal here in the unites states, but then again, air bags can be to if they wanted to get picky..
There isn't really that many downsides to bags, of course for the first couple weeks you're working out little bugs and kinks, such as leaks, ride heights, pressures, etc., but after that, they're fun as hell..some of the reactions are great, my gf always calls my truck a freak show because when you pull into a parking lot and lay it out, people just stop and stare..