I've only been through ATL once since Breezeway was implemented and it didn't work as planned as far as I could tell. I like the concept, however, of being able to walk up at any point and board without having to cut the line or wait for zone 6 to finish boarding.
When I arrived at the gate for my connecting flight, the lane was full of families with strollers. It appeared they were queued for the standard pre-boarding ("families with small children," etc.). Wheelchairs were pre-boarded, stollers were not.
The GAs didn't seem to have a good grasp of how things should work and ended up calling Zone 1 as they had before. As the Breezeway lane was clogged, I went the regular line. The families started to board, cutting across the regular boarding lane to the BP reader and one family had Z1 BPs, but the others didn't and were told to wait until their zone was called.
I boarded as I would have normally. I didn't see any advantage because the GAs weren't managing it like I thought they should have. That is, they should have educated people in the gate area with announcements of how it worked, but they did not. It's not going to work unless people know how it works.
Then again, I've lost track of the number of Zone 7 pax I've seen walk up when Zone 1 is called even though announcements about zone boarding and how it works are called out repeatedly before boarding.