I've used Private Auctions and I kind of like it.
Pros;
Great for "holds" on items.
---Auctions are set for 7 days. So you can hold an item for a price for 7 days.
Also auctions takes your item away from your hoard.
---Current CR does not do that. It counts each item as 1. So let's say you're selling tons of festival currency and you have 5 trades going on.
You sell person A a 99x stack and person B wants the same. You accidentally chose the same one. But person b accepts first and Person A took too long so now their CR is moot.
You'll notice a lot of Dom shops/accent shops won't accept 2 ways for this reason.
So Private auctions are perfect for holds. Bc you can set it up and forget about it. Not only that but the auctions don't take out a percentage ,I'm not 100%, and it's perfect for a big transaction of same items.