I have a 551 Rev E that was mounted on an hk-94 used very,very little. Unit comes with new batteries,box,manual and all factory accessories.
I can sell it for $300 shipped or would like to trade for a 552. I have another 552 and have decided to keep the battery models the same so I can switch batteries between the two and not have to worry about two sets of batteries. I have a picture for those interested. Paypal accepted