The Honda Manual advice to use a thread protector for joint removal, but its pretty expensive
I found similar nuts for much cheaper but i was wondering whats so special about the OEM one. Genuinely curious.
Does the OEM one shape allow for larger area of contact or something ?

 

You don't need that at all. Unless you actually hit the threads, which I don't see why you'd want to, you will have no issues. Obviously you just wanna take care not to hit the threads whenever you are disconnecting a ball joint. I use a Pittman Arm Puller when disconnecting most ball joints. It works the best. When I can't get one on, only then will I use an actual "ball joint separator".