Some Monster Life's Inquiries

I'm a Paladin.

My Blast critical hits 100% of the time so Horntail is useless for me until Red when I actually need to use Charged Blow for that specialized skill and Blast buff.
As for Zakum.... chance to block attacks? When you take Guard, Guard, Guard, Guard, Guard, Guard, Guard, Guard, Guard, Guard, Guard, Guard, 1, Miss, Guard, Guard, etc. the chance at block is also useless.

..and they are not cute! (if you ever consider that )

Monster Barn Expansion is the thing that gets me confused because I'm not sure whether it increases your monster barn slot by 1 for 8 gems or instantly maximize your monster barn slot for 8 gems (that would be too good to be true) ?

Also, nobody have an idea for the question above? I'm going to spend a number of gems to buy either monster slot expansion or monster barn expansion, but I'm not sure which one is better.