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 thumb screw.
Spools,well are just spools, they come in plastic, ABS, Delrin, and Aluminum. It's best to avoid the injection moulded 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.