1) It uses a persistent connection rather than several transactions, so you do avoid the overhead associated with establishing an http connection several times. That may actually be significant. The actual effect will depend on several factors, including how many connections it saves, the number of concurrent players, and how much state is maintained on the server.

2) In addition to stratus, adobe used to have a beta thing called cocomo. But they've apparently turned that into some livecycle collaboration service, which is of course not free.

Player.io also provides lobby and room stuff, and they have a free account level. I'm not sure whether the free level is appropriate for multiplayer. Server-side code must be done in a .net language.

If you're rolling your own solution, lobbies and rooms are just a matter of designing your db and interface correctly. Not to say it's trivial, but it's not exactly breaking new ground either.