When you are doing drift diving, as in Cozumel, or Indonesia, or sites in the Pacific Northwest, one of the biggest LIKELY problems to have is to be blown away from the group or the guide. In that case, you need to be able to signal your whereabouts. The best strategy is to deploy an SMB from depth, the moment you are aware you have left the group; this will give the dive boat the best chance of seeing that you are moving away before you are too far to spot. But deploying an SMB from depth is a skill that requires a fair bit of buoyancy control, and has risks involved (if you get tangled in the line), so if you have no opportunity to get into a pool or anything and learn to do this, you might be better off with the simple kind that has no valves, but is simply inflated on the surface. It's better than no signaling device at all. But if you like drift diving and think you might make a habit of it, acquire a good quality SMB and learn to deploy it from underwater.
My personal recommendation, although I recommend very little from them, is the Halcyon bag. It is easy to inflate orally, in warm or cold water, or with an LP inflator hose. The bags are sturdy and the hardware is good quality. They are expensive, and worth it.
