While the BD+ interior construction 'looks similar to' P1, as river_rat's filter testing and dissection confirm, it is clearly not the same.
River_rat's work is well respected here and I'd trust his observations and conclusions. That and I've used the same application and concluded the same.
Psh...Back in my day, you could get 4 of those for $16 after rebate if you knew the secret codes errr I mean lingo for the advanceautopa... I mean black market. Heh, kids these days and their 'price' complaints.