These are already available on FamilySearch, which has 1,161,877 records transcribed. Unfortunately ancestry doesn't show the number of records on each database on their "New and Updated" page any more, and if you leave all search fields blank, it comes up with zero matches instead of the total number of records like it used to, so I'm not sure whether ancestry have transcribed these themselves or if they just have what FamilySearch have transcribed so far. Both sites also have browse facilities.
Norfolk BT's are unlike other counties in that most years Archdeacon's Transcripts were sent instead, so the BT's for each parish are fairly sparse. Ancestry and FamilySearch both have browse facilities for the AT's.
FreeREG have done a lot of transcriptions of the Norfolk PR's, AT's and BT's, so you may well find an entry on FreeREG and then you can browse to the image on ancestry or FamilySearch using the FreeREG info to find it.
BTs on ancestry
BTs on FamilySearch
ATs browse on ancestry
ATs browse on FamilySearch
My guess is that ancestry have not transcribed or indexed the BT's themselves but are just using FamilySearch's transcriptions (not complete yet), as I would have thought they would index the AT's too if they were doing the work themselves. Let us know if you find evidence to prove or disprove this, please!