It seems only a couple of years ago that it was difficult to find a good SMB reel, but now we are spoilt for choice. Our list includes a number that were not originally designed to be attached to SMBs but adapt well to that function.
Because reels are such a good way of carrying a good length of line in a manner that allows it to be deployed and recovered quickly and easily, there is a growing tendency to carry a compact reel during a dive, perhaps to act as a distance line for wreck penetration or for low visibility problems, and to assist in deploying a delayed SMB at the end of the dive.
Reels for cave diving are specialised items requiring technique to match, and some of the reels listed will fit this bill equally well.
The problem to be aware of when selecting a reel is that the drum and/or line can jam or snag, so you need to ensure that the line has a clear path and that the drum is free-running and not over-filled with line.
Bear in mind too that some reels are distinctly left or right-handed.