Slizzardman, Slizzy or Liz noted the BL puts a lot of pressure on the inner elbow which is quite tasking as our inner elbow typically isn't subjected to such things naturally while the outer elbow (where FL hits a lot) is typically fine.
Notice that the GB WODS, generally go BackLever, Planche, FrontLever. I used to go Planche, BackLever, then FrontLever but I guess it switches from push to pull exercise.
However, I also played with FrontLever, Planche, then BackLever and that made the BackLevers really suck hard.
Your elbows only hyperflex if they do because you have hyperflexion in your elbows. Still, you are putting load on the elbow. There are quite a lot of gymnasts out there performing crosses and ring handstand or cross handstand with funky hyperflexed elbows with no problems.