The reticle on the M110 leupold scope is an illuminated reticle, and yes, it does introduce something else to break in the field, but the reticle will continue to work if the battery dies or the illumnation fails, it just will not be illuminated.
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Not that you use the back up sights much, but it is still nice to be able to zero them, and then leave them mounted when you put the scope on for use when all else fails.
By Melvin Ewing October 16, 2014.
Some of these downsides are that they are not as well suited to the traditional sniper role due to their shape and the fact that they fling brass all over the ground which can compromise your position and potentially leave target identifiers, not to mention.