Many people feel they're tidier, particularly if you want one in the backyard. However, the quality of the enclosure is important. Plastic shells can be damaged easily if you're not careful, and some are criticized for poor mechanisms. If they jam, you might have to disassemble the case. It's certainly not a problem with all enclosed air hose reels – some are praised for how well they work – but an open reel has fewer things that can go wrong and they’re generally considered the professional option. ;