Hi dubkarma,
I have a BP25 along with several other Bryston components.
I have both the BR1 and BR2 remotes. I have both because the BR2 cannot control the BP25.
While the BP25 and BP26 superficially seem nearly identical except for their power supplies, a difference is the remotes they can be used with.
On the Bryston website, these are the compatible preamps listed on the BR2's page (note that this list includes out-of-production products):
BP26, BP17, BP16, BP6 Preamplifiers
As mentioned above, the functions the BP1 provides are mute/standby, volume and phase.