To me it is really about how much to you use your rifle and in what conditions and manner.
If it is a duty weapon then AA are worth the extra money upfront. If it is a range toy Zombie killer that sits in a safe 99% of the time I personally do not thing that you will recover the difference in the upfront cost.
N batteries are cheap if you know where to buy them and 70 hours for the average shooter is a lot of range time.
The other part that has not been mentioned is that the footprint on the rail is smaller in the 551 and this IMHO is better if you are going to co-witness the optic and BUIS.