Hi Tom, Ryan from Pear here. AdRoll did not have the Facebook Exchange option when it was available, and we saw Perfect Audience had it first. Also, I do have the same conversion goals set up in AdRoll as I do in PA. (/checkout_thankyou.asp), and they are not firing properly, even though in Analytics I do see some conversions.
I'm happy to devise a better experiment with you and run our next customer on both platforms with the exact same criteria. Email me if you're interested ryan at pearanalytics dot com.