Exactly. I'm willing to bet that divers who do a variety of kinds of diving own a variety of spools (and maybe even SMBs in more than one length). If you're doing wrecks or otherwise deep dives, take a larger spool, or a reel. If you're being led around by a DM in Cozumel on the sites dive ops take the average diver to, you may rarely need to shoot an SMB at all, and if you do, you could almost always ascend to 20 feet and shoot it there without being swept away from the boat. (At worst, another boat finds you--you will not end up out at sea.) If you're doing advanced sites in Cozumel--something I haven't done--then take a larger spool. The average vacation diver doesn't know how or doesn't feel confident shooting an SMB, and the dive ops are well aware of that. The last liveaboard I took recommended divers carry an SMB with 20-30 feet of line attached. I have also seen leashes advertised that I assume are similarly intended to be deployed at safety stop depth. It's great that we on SB are among those who find shooting an SMB from significant depth to be an important skill, but I would try to keep in mind that it's not really expected or necessary for the vast majority of "vacation diving." I don't use the term "vacation diving" in a disparaging way--it's mostly what I do, because I really love it. I summary, I think a "small" spool with 100 feet of line should cover most of us vacation divers in the most likely scenarios.
I noticed Light Monkey has a "mini" spool with 25 feet of line. That could be just the ticket for some of the lazy vacation diving I do. Cozumel--I might want more than that due to the likelihood of current. Just sayin'.
@uncfnp , what op are you diving with that you find yourself shooting an SMB so often? I don't think I have ever seen another diver shoot an SMB in Coz, though many of us carry them just in case, and of course there are people on SB who will tell you they have "needed" to shoot one in Coz on average every so-many dives. If you're doing it just for practice, with an op that is okay with that, then I suppose that makes sense. I have been under the impression that most ops would rather divers not deploy SMBs because it could become confusing.
I'm just gonna stick with the 100 feet spool that I already got. I suspect it will be ok. If not, I'll just get a bigger one later. I always try to make the correct choice initially, but I've learned that I'm picky and I won't know what I will like until I actually try it in action.
In reality, I will only be doing warm water vacation diving in the foreseeable future, either in the Caribbean or Southeast Asia, land-based or liveaboard. I know that I won't be using it on a regular basis, but it's a good skill to have, and a skill needs to be practiced. I have shot an SMB at depth (30 feet) a grand total of 1 time in Cozumel, and that was only because I told my DM/instructor I wanted to learn to shoot it. I got to do it once, and my husband got to do it once. I wish we had done it several times, but it was not to be. While my next liveaboard trip will not require shooting an SMB (it has a hang bar and little boat traffic), I will notify the DM and captain that we intend to shoot ours after every dive as practice.
I also dive with 3Ps in Cozumel but my husband always insists on hiring a private DM, so it's not like we'll ever need to shoot our own SMB unless we get separated from him. But if we do get separated, we'll be ready!