It's very strong, IMO. One of the best combos I've seen in 5th Ed is two fighters with good ACs and the Protection style fighting side by side.
Disadvantage is just brutal when against good AC. When foes need luck to hit you, giving them disad REALLY hurts. And when they can both do it to one another...dang. But even without that, it's quite good.
[MENTION=6776182]JustinCase[/MENTION]
I'll have to think on it...brains kinda mush today due to pain meds. Do you have a few ideas? Maybe I can help you flesh them out...