The click part seems to apply to all the off the shelf fittings, and to even the molds up to the P power. The receiver just snaps in place with a click. The sleeve name probably comes from the shape of the fittings. Instead of looking like a mushroom they are just a hollow sleeve. The other unique part is that they are oval shaped rather than round. They look surprisingly like the custom mold shape i got. The difference is that the sleeves are very thin and flexible, while the molds were solid and not so flexible, even though they were made from silicone. Here is a bit of a write up on them. I think they are a good idea. If you believe Signia the closed sleeves provide more feedback isolation than even double domes.
Signia Click Sleeves for RIC fittings improve audiology and usability