Reelscome in two main varieties, a ratchet reel mainly for deep SMB deployment and the standard reel for cave & wreck line laying, this version does not have a ratchet and locks with a thumbscrew.
Spools,well are just spools, they come in plastic, ABS, Delrin, and Aluminum. It's best to avoid the injection-molded plastic as they break easily. It's also important you don't buy a spool with too much line on it or it will obscure the holes. If you are using thick gloves you might want a larger finger hole.