I for one will be looking forward to a B&T vs Bren 2 review when the NR lengths become available.
B&T - short ejector pivot vs CZ long ejector pivot. difference balance of ejection cycle force. Bren has shorter push rod than APC
APC uses the barrel trunnion block as the single center piece for the handguard and barrel using 6 hex bolts. The hanguard is bolted down to the trunnion with 1 bolt on top and 1 bolt to the bottom. Bren uses 4 bolts - Bren's handguard is actually 5 pieces that bolt each piece of the barrel block and the barrel itself. APC is quasi free floating and Bren 2 is like SCAR and old PWC, the barrel is bolted to the handguard.
APC's gas block is a bar stock, Bren is mostly a forging. Bren is lighter because its gas block and barrel trunnion are smaller and less massive than the APC. CZ bren receiver is also more complex in geometry and APC avoids all that, ie subtractive vs addictive approach.
They really are the same thing just slightly different execution of the same idea. I will say that B&T uses lots of massive blocks because their volume didn't warrant forging, but APC 2 pinned lower and upper is much more KISS and robust than Bren M2 method
The CZ Bren M2 also has too short of a hanguard, not enough space to mount LAD and light, APC's longer handgurad is a bit better, some where in between the MK18 and the old KAC estate wise.
APC uses AR15 trigger pack and the new one uses AR pistol grip - this is a big plus if you want to retain and train for AR trigger if you go to the states to compete or your work gun is an AR or C7. This is a major selling point of APC.
Too be honest, I am not quite sure there is a 1000 bucks difference there no matter how your cut it if you purely look at dollar vs value. But if you have to retain and maintain AR trigger memory, you may have to choke up that money for the APC.
Finally, amongst all these guns CZ Bren M2 is the only one employed and approved by NATO - this means it passed certain standards.