It's definitely a good system. An infant system, with many tweaking to come until it is solid for sure, but a good system. Now if only console marketplaces would follow suit.
I haven't needed to use it yet. I didn't preorder Arkham Knight, based off WB's previous releases, which I think I should have just to test the refund process out. I see it as a extremely useful system which takes the load off Steam's customer support and places the fault entirely with the publisher.
I used it with Ghostship aftermath - Did a writeup here - Cheskitech - Steam Refunds – A Good First Experience