The HD Zumo 550 is the same as the regular Zumo 550, just sans the HD logo
Same as the Quest 2 and the HD version, same same.
My Zumo 550 came with both car and MC mounts, works great by the way.
I can't see any reason to buy the H-D Zumo instead of the regular Zumo 550. The Harley Zumo ($799.95) does not include the handlebar mount ($79.95) nor the automobile mount ($119.95). \\; The regular version of the Zumo 550 includes both mounts and can be found online priced at around $650, sometimes even less. There are no additional features on the Harley version. I would also be leery of the H-D version's compatibility with future Zumo map upgrade disks\\; they may have issues with the regular Zumo upgrade disks. (This last concern is pure speculation on my part. I've seen some problems with the BMW Zumo version mentioned on the Zumo forums.)
I doubt that compatability will be an issue, since even in the HD instructions it says to go to the Garmin Zumo 550 site for further info and instructions and gives their website link.
That being said I'd buy it if I wasnt so cheap.