I don't have one but I've been very interested in getting one so I've done the homework.
Yes, it needs to be removed before cleaning but when it's reinstalled it retains it's zero. Also, according to my sources it has a backup sight under the rail.
COULD SOMEONE WHO OWNS ONE PLEASE CONFIRM THIS
EDIT TO ADD: OOOPS! see post number 5 in this thread. - your answer is here.
Jeff