I use a Simply Attached Sling, but am thinking of getting a Moby IF I find the SAS is too hot for summer. So far not a problem, but it's April!
My dd is only 11 weeks, so I can't answer size questions.
Once you're used to it, tying up is no problem. I have been experimenting with different ties of late, and they take a little longer. But once you have your favorites, you'll be able to do them in your sleep. It does take longer than a ring sling (or similar type), but not THAT much longer.
I pop my dd in and out all day long, leaving the sling on. It's part of my attire now. I get a few looks when I still have it on and dh has baby, but that's OK!
Zia+Lane+Sonora=Mi Vida Loca! :