Do the benefits from having the circle of the shepherd apply to the creatures summoned with the bag of tricks? The extra HP and magical attack when it comes to weaknesses and resistances.

Mighty Summoner specifies that the creatures must be summoned by a spell to receive the benefits.

Bag of Tricks doesn't use a spell to summon creatures.

filcat, would you then suggest it should work with a magical charm conjure animal as it is 'as the spell'?

(as you have have /are running ToA you can see how that might be awesome / scary)

Quote from Moondruidsneversleep >>

filcat, would you then suggest it should work with a magical charm conjure animal as it is 'as the spell'?

 Yes, anything that says "cast a spell".