Ditto re: using just the stones. Got them because I thought they might help me avoid building a false bottom on a GBD that was drilled high. Was entirely satisfactory for that purpose, so, kind of intrigued, I have started playing around with them in "no problem" briars. I find them to be a marginal, but noticeable, improvement. Anything that dries out a smoke without cutting down on the draw is worthy of some note. I can pretty much smoke anything in anything with no real issues, but I can see where these might also help if you have issues with packing a particular type of tobacco, such as flake or shag, by keeping the airway open.
I am not a fan of gimmicks in general, but I haven't found a downside to using these little devils. Looks like a bag will last for many months, an some people say they can be reused.