They are rather basic in their design. Anti-drainback valve is simply a rubber ring sandwiched between the filter cartridge and the machined inlet/outlet body. Not a whole lot different than a disposable can filter. The cartridge seals to the end cap with an o-ring for the ID of the cartridge and the OD of the end cap.
In my limited experience with these, the ends seal well and the oil has nowhere else to go but thru the media. Mine sealed so well that the cartridge bulged a bit on the ID.
http://forums.pelicanparts.com/911-engine-rebuilding-forum/706984-engine-bearing-failure-disassemble-heads-too.html#post6987246
The above incident is what prompted me to bring up the question about filter flow capacity. I wasn't very inspired by Canton's belief that engine assembly lube products created additional restriction. The oil I used was straight 30W for initial break in.