Same internals etc and just lack of packaging/instructions?

Fairly sure it's just the pretty box you'll miss.

Possibly the cheaper models may have some 'tweaks' to hit a bike makers price point, but I've never come across spare parts for their brakes that are dependant on OEM/retail.

ive never come across spare parts – other than brake pads and springs 😉

its just a box and aftermarket ones usually come in pieces and need bled !

It can vary. most are the exact same but without the box

occasionally though you will get ones that are different. To meet a manufactures price point or their own spec.

The only vital thing that may be missing is a spare olive an insert if you need to shorten the hoses, although they cost about £2 each if you need them.