If you wanna sextant block Shaped Atoll and run only that, do it. If you wanna play like Alkaizer that doesn't sextant at all just run random maps, do it. People like Grim or CuteDog will still grind easiest maps for their Headhunter and find the fastest clear speed build out there and run that for currency. Why limit that? Cause sextant blocking is harder to grasp? It seems to me that if more items/currency are in the game, everything is cheaper, so that makes it easier for casual players to gear. Do you want to poe buy items? If you do, you can visit U4GM to have more guides and methods about this.
1) Recipe only use rare and unique beast. Blue or white monster are not used in any way, but they still count as 1 beast slot in your menagery. And you have absolutly no possibility to remove this kind of beast from your menagery except transforming them in currency (which cost 1 chaos per orb). They can probably be removed from your menagery by higher level beast. I can't make so much comment on this for the reasons I explains before.
2) The menagery is an area where fight take place. So you don't have your stash in it. This force you to take currency in your inventory in order to buy some specific net, like the one used for trade beast. And while it's an area where you fight monster, even if you are not in the arena, you can be killed. Some HC player had this cool surprise while requesting a beast crafting from other player and waited them in the menagery instead of their HO.
3) Except all of this, recipe from bestiary league introduced many cool things. The menagery looks realy cool. It's a realy interesting crafting system and unlock many cool possibility. Beast in map can be realy challenging, and sometime realy powerfull. It's a realy interesting challenge from this point of view.
In conclusion, the beasts and recipe introduced add some realy interesting points. But at the same time, in terme of realisation and gameplay, I honestly, I didn't played a less intuitive system in a game for a long time. I sincerly tried to do an objective review and tried to not sounds like a professionnal whiner.