A/B Split Testing in Campaigns?

I'm fiddling with proper A/B split testing in campaigns. I think I can do it by setting up an automation that gets triggered when a tag is added to a subscriber. It would then split the list 50/50, and then send different campaigns to each group. I could trigger the send by bulk adding the tag to my entire list.

Would this be the best way to do this? Any caveats? Better ways to properly A/B split test two different emails? It's a bit clunky this way, but I think it would work?

May eventually try this on a list of 150k.