The capstone ability is particularly lackluster, granting a fairly small bonus in a fairly small sub-set of circumstances. It's certainly nothing like the fighter or barbarian, or even the paladin.
Biggest problem with Beastmaster is that... you can just buy trained animals.
Pros:
Don't have to spend as many actions.
Can have more than one.
Not restricted to CR 1/4.
All the benefits of being another archetype.
Cons:
You have to make Handle Animal checks.
They don't get your Proficiency to AC, Attack Rolls, Damage Rolls, or saving throws.
No sharing spells at Level 15.