My experiences with reefcleaners have gotten progressively worse. I paid extra for overnight shipping in an attempt to mitigate losses, but the way the snails and hermits are packed plays a big role in the survival rate. For example, about 25 astrea snails were packed in a bag and I think it only takes one dead snail to take out the entire lot. I ordered a bunch of hermits and lots of them were dead, where the bodies have come out of the shells.
John just credits back the dead CUC but doesn't cover shipping (makes sense), so you're rolling the dice. If you order say 50 snails at 75 cents each and pay $50 for overnight shipping, and half of them are dead, you just paid $2.75 per snail. Even at 100 snails with 50% loss it's still $1.60. In order for them to be cheap, a majority of them need to survive.
If you have a small tank and don't mind small snails like ceriths, then reefcleaners may be the way to go. But for a larger tank, it's not really worth it. I ordered a ton of ceriths once and after a few weeks my sandbed with littered with cerith shells. I know it's tempting when they're only 12 cents! Looking at a tank with tons of little snails is not very appealing to me though.
When you go to a LFS, you can pick out your CUC and ensure that each one is alive. I don't mind paying a little bit more for that luxury.