I bought mine off the shelf from the dealer for my 08. It works fine, though you do have to give it a good push. PM me if you need a part # and I'll try to dig it up.
I installed the smooth one on mine friends 08 Ultra and had no problems at all and the one with the key should be no different. One has key and the other doesn't. Same install directions.
To all interested, I purchased the push button/locking fuel door release today (53842-00B)for my 08 dresser. In my opinion this was a no brainer. I made NO modifications to anything, changed them out, and it works perfectly. It lifts the door open about 3/8in by itself. The only variable that I can think about, would be the hinge spring tension could be different from machine to machine. I know about the uncertainty, but unless I was very, very lucky, I say go for it.