We used our DuoGlider with our kids who were 3 and 1 on our trip last summer. Getting it on and off the buses was a pain the first few times but once we got used to it it was pretty easy (I definitely couldn't have managed it plus the kids myself, though--you definitely need one person to take the stroller and one to mind the kids). In the parks it was a godsend--the big canopies and basket were really nice to have, and we had no problems at all maneuvering it through stores, etc. We appreciated its surprisingly good one-handed steering. The only thing that got to us was that one of the canopies kept popping off. That was pretty irritating but I'm not sure if that was just our particular stroller's problem. And, oh yes, whoever was riding in the back would sometimes kick the back of the seat in front or start pulling the front seat rider's hair; that called for some minor disciplinary action but wasn't too big a deal.
I use a super lightweight stroller at home for our toddler (our preschooler never uses a stroller except at WDW) and am not planning on purchasing a Sit N Stand, but it sounds like the Sit N Stand might be a good alternative to the DuoGlider at WDW, depending on your children's needs. I'd definitely suggest going to a baby store and taking some good long test drives with the strollers you're interested in. Happy shopping!