We have stayed at BC many times, but will comment only on the service from this year. We have done 3 split stays this year that have included BC, April 2018, November 2018, and February 2019. Both April and this past February the buses were great. Never waited more than 13 minutes...and the 13 minute wait was when we just missed an MK bus as we walked up to the bus platform. So bus service time wise was consistent. The November trip wasn't quite as consistent....but we were there for 2 weeks through Thanksgiving ( holiday week, so may not be a good representation.) The bus crowd wise was a different story. I feel like the buses the past two years are incredibly packed....like sardines. As long as everyone could fit behind the line the bus was a go, but honestly it was dangerous. A couple of trips people would fall when the bus would come to a stop( a man holding a stroller couldn't hold onto a rail, the bus stopped, he lost his balance. He fell then the stroller fell over on a small child standing.) It has been like this almost every trip for the past two years going to MK on the buses. Coming back to the resort the buses at midday are rarely filled. I can't comment on evenings after fireworks though, as we have skipped these for the past 2 years since DD was born. Hopefully this doesn't impact your trip. We LOVE BC, it is our resort of choice. I hope you have a great vacation!
I will edit to add, I hate resort changes without a vehicle. We don't live overly far, so normally drive. On our November trip we chose to fly, as I thought it would be easier with the baby and older son by myself.......it wasn't! Changing resorts was a pain without a vehicle to move myself....and Magical Express...yeah...never again! It probably wasn't that bad, but what would have been a 3 1/2 hour drive home ( had I taken my car) turned into a 7 hour journey home because of leaving early due to ME schedule departure for us.