I've used the Baby Beast RBA head and it works great, but it will not solve a leaking problem. It's more likely to invite one, especially when you're still learning the right way to wick it. Once you do though, you gain a lot more control over how it vapes and tastes, and with SS coils you can use temp control. That's not yet possible with stock BB drop-in coils.
The Big Baby full kit includes the RBA. The baby Baby needs a separate purchase because it needs an extended glass section to fit the larger head in the tank.
I also have a TFV8 RBA (not the Baby) mounted in a Geekvape Illusion tank. That thing rocks.