abirdcall
(she/her)
I'm not sure if we are looking at the same feat.
For a non-Beastmaster Ranger, it looks like a very good feat. If both of your weapons are light, and one of them has the nick property, it looks to me like you can add two attacks to your standard allotment.
Ex. level 4 (to keep multi-attack out of it) -- you have one attack with your primary hand. You make an additional attack with your off hand, that (due to nick) is part of your attack action and not a bonus action. You have now made an attack with two light weapons as a part of the attack action. You may now invoke the feat and make one (further) extra attack as a Bonus Action later on the same turn with a weapon that is different from either of the two weapons you have already used (and each is different from the other). It's not clear to me how that wouldn't work, but if you can explain it, I am certainly not an expert.
A feat for a bonus action minor attack is quite poor. Polearm Master gives you that and you don't need to take a fighting style to add your proficiency bonus to the damage. You also get the reaction attack.
For a dual wielder I would always take Mage Slayer over the feat or even Defensive Duelist.
You already have a use for your bonus action as a Beast Master so you gain nothing with the feat.