I have a mixed Apex1 and a Force1 setup. Basically everything is the same. Obviously, the Apex shifters/cassette have one less gear, which isn’t a big deal. There is no performance or functional difference between Apex and Force.
Otherwise, the biggest difference is the RD. It is steel instead of AL, this means nothing functionally. The other difference are the jockey wheel bearings. The Apex basically doesn’t have bearings, while the other versions do. You’ll want to change these after a season anyway, and nicer jockey wheels are super easy to swap. I’d say the SRAM jockey wheels are tough to clean, so pick up some flat AL wheels on Amazon which you can clean the mud off of easier anyway. Otherwise, the Apex RD is 1/3 the cost for no good reason - perfect for breaking during CX.
The only reason NOT to go full Apex is the 10 (EDIT - APEX is 11sp now) vs 11sp if you’re swapping wheels around. In this case, you can just get a Rival/Force/S-series rear shifter and cassette. I’d also argue that the Apex paint job is nicer than the Rival, which is purposely ugly.
If you’re in the UK, why would you go for that offbrand bike when you can get a equivalent Trek or Cannondale for the same price? https://www.sigmasports.com/item/Cannondale/CAADX-105-Disc-Cyclocross-Bike-2020/MV01
The benefit would be that you’d get a hydroformed AL frame instead of a butted frame, which will give you a much better ride.