If we're talking about Matco impact swivel sockets I have them in 1/4, 3/8, and 1/2 drives. The pinless design is simply the best you can get in my opinion. There's no pin to break or fat retaining collar (Snap on). The design gives you a lower profile and better socket rotation in confined areas. They are extremely expensive off of the truck, but Ebay can be your friend.
Unlike the MAC design where they put a square part into a round hole, Matcos design works well. There are those people that will say only Snap on will do but, this isn't the case for impact swivel sockets.
You can find the similiar design in Craftsman and Armstrong impact swivel sockets but, their overall height is taller, the available sizes are fewer, and they're still fairly expensive unless you score some on Ebay.