They couple up to the 805's with no issues.
If you are trying to mate them with the 3 rail couplers (claws), there is an issue. The knuckle doesn't open up enough to get a tight fit with the claw like the 805 does. A little work with a file will solve this, sometimes just the kadee, and sometimes the claw needs a little clean up too.
If you plan on a switching operation where you will be uncoupling cars with some sort of Kadee magnet (not your hands or a tool), there does tend to be a bit of an issue with the new 700 series couplers. Making sure the trip pin is bent at the correct height is an absolute must. Even then, they will have some problems opening far enough to get the "delayed action" to work properly when you want to shove the cars you just uncoupled from. The 805 has much more movement in the actual knuckle itself, making hands free switching realitively trouble free. I haven't figure out how to get the same from the 700 series .....yet!
So if you're not concerned about switching or coupling to three rail couplers.... 700's all the way.