The common ones folks keep are full black, black/pink & tiger tail variants. Of course there are others available just not as common/popular.
Once in the tank, the black & black/pink ones 'appear' more often. Tiger tail ones tend to hide in the rocks & come out at night.
IMO, they don't really do much cleaning up as they move quite slowly. Nevertheless, they are a nice addition just for the variety. I have 4 sea cucumbers in my 5ft tank. They have been handled quite roughly on my side & wrapped around the wavemaker to eat algae - never had an issue with it spilling its guts.
About the defense mechanism of spilling its guts - it does happen as I've seen it in coral farm's tanks. Possibly stressed from shipment.