Are they worth it? Perhaps, but it depends what you get... problem is usually they're overkill for your tank, I can't comment on any specific packages you might be thinking, but typically they do about 1 hermit crab per 1-2 gallons of water, 1 snail per 1-2 gallons of water (depending upon the kind), and maybe a couple serpent stars, or cucumbers or something depending upon the size of the clean up crew. This IMHO is overkill, as they may be great right after your tank cycled with live rock, has brown di
atoms all over the place, dead matter on rocks etc, unfortunately when most of that is gone your tank stabilizes and stops making so much "food" for your clean up crew and they end up dying.
Ok I just looked at liveaquaria's basic algae attack package and they give you about 1 snail per gallon, and a lot of mexican turbo/margarita snails. If they're the true mexican turbo (golfball sized) then these are great but 50 in a 125 is WAYYY overkill, if they're the margarita snails (they might be a cold water version.. lots of debate goes on over this) they aren't that good.
Bottom line, if you want a cleaner crew and it seems that a package is cheaper than if you get in individually, buy one that's 1/3 the size of your tank, ie you got a 100 gallon tank, buy the 30 gallon setup. Personally though I think its just as easy to get a bunch of one particular kind of snail/crab/whatever WHEN you need it, then you won't be stuck with a bunch of junk you may not need. Not everyone wants hermit crabs in their tanks, not everyone wants sand sifting stars either.
