I don't have them but had the 518's. The 508's are a bit narrower but have more pullback. I hated the 518's because the hand position was awful - kind of the like the old time early 1900 Harleys. From the looks of the 508's, they would be even worse. I tried to convince myself the 518's were comfortable but after 6000 miles while in Myrtle Beach, I finally said enough. Took them off as soon as I got home and installed 504's. Of course I have long arms (36 shirt sleeve).
I have the 508's and like them very much. Yes, very similar to the RK Custom bars, but a little different at the grip angle. I am 5' 9" and they are just right. I can now sit back and relax. Also put on a Corbin Solo ala Mr. 8 Ball. I also did the internal wiring and braided cables.
:dunno: What kind of cables are you guys running with those 508's? I just spent some time at the dealer, was going with Harley's new "Diamondback" series at stock length, but they would not work on my bike (1999 FLHRCI) with the MM injection. I had heard some good things about the Diamondback but the search goes on. Are you running whatever at stock lengths? I used the stock length when I put them on but wanted to check now that I am going braided. TIA, Mark