Single or multi-BB spring shotguns are great guns that will operate effectively in any temperature. The good quality ones tend to be pretty reliable and durable too as they have very few moving parts to break, so there's really less to go wrong with them.
The good shotguns tend to be quite accurate and really shoot more like any other airsoft gun than a shotgun, even the multi-shot ones. You could easily put an optic on single shot shotguns and almost use them as a sniper gun. The multi-BB ones don't really spread a whole lot and can be quite accurate even at a good range. You can get a better spread for close-range use by mixing BB weights in each shell.
Personally though, I think they're better for more experienced players, especially for outdoors use. Having a single shot pump action gun can put inexperienced players at a serious disadvantage against even noobs with AEGs. I know I couldn't see myself wielding my shotgun in a game as a primary. Slung over my back to use as a secondary, perhaps, but I know I would get my ass handed to me in an engagement with a shotgun. lol