I like the idea of talking to Yeldon. The Bills at least have to look into it. It gives us a near pro-bowl caliber player at EVERY position in the secondary.
That said, if the due diligence turns up that he is a pain in the a**, and won't play zone (as oppossed to not wanting to play it for blow-hard st. doug), then that's a no.
Also, I wouldn't part with a 1st for him.
Here is a list of UFA Cb's next year: https://www.spotrac.com/nfl/free-agents/ufa/cornerback/ (not sure if there are many good ones on the list).
There might be other CB's up for sale near the trade deadline that will be a better fit for the culture.
Now, I'm in the do the due diligence camp, but I don't envision a positive report coming from that, or the trade price being okay (I'd do no more than a 3rd).