Just having a little look over this thing and in some respects it seems superior to the summoner synthesist.
Now unless I'm completely mistaken this ability is ONLY granting the evolutions the same as if a summoner was able to cast Evolution Surge on something other than his Eidolon.
i.e. we're not calling up an eidolon we're just making the animal companion "Hulk Out".
It also means when the companion dies or is removed for whatever reason the Hunter is now the one doing the "Hulk Out" but he's not getting some eidolon shell he's just evolving his own flesh.
plus its a swift action so extremely helpful for not wasting my actions buffing once combat has started.
So you can have the evolutions without the shell meaning you can keep wearing your armor and gear unless of course your changing size or shape with extra arms and legs and then things might get a little tight under that breastplate if your not careful with your choices.
But still this is basically swift customized polymorphing for a martial weapon prof , medium armor character , 3/4BAB sure but (Ex) ability score increases which can stack with enchantments.
Seems like a pretty fun deal and dare I say the Summoner Synthesist concept done right ?
Round 2, begin!