Well I never hesitate to buy from KEH. They have always done right by me and have always been very conservative with their ratings. I just bought a Nikon 50mm lens from them that was rated as Bargain grade, when I got it, you'd be hard pressed to tell it from a brand new one. My own Hexar came from the RFF forums, but the nice thing with buying from KEH is that you get a 6 month warranty in case something goes wrong.
Only you can decide how big of a deal the flash is. I just got mine (from KEH no less) about a month ago but I've yet to actually use it. I've done a few snaps here and there, but more often than not it just stays in the bag.