The Marlin is indeed a great gun for the money...I had a used one for a spell and liked it alot; unfortunately, it developed serious feed troubles for no apparent reason so I gave up & sold it. A friend of mine has one and it has performed flawlessly for him. I can definitely say the iron sights on the Mossberg are superior to those on any Marlin semi-auto I've seen; even the fancy SB version I had with it's buckhorn rear & Widescan red front wasn't particularly good in my opinion. The little Mossi also appears to be a good gun for the money. Another friend has one & to my knowledge has only experienced issues with it when it has been shot alot and not cleaned for a while; I find that to be true of any semi-auto rimfire regardless of make. The Marlin is a bit more money, but has a larger capacity tube mag (which I like) and is made in America, whereas the clip-fed 702 is a Brazilian import IIRC. The Mossberg is slightly handier and easier to use, at least for me, but I think the Marlin is a better built rifle, and possibly more accurate in the right hands. I don't honestly think you could wrong with either gun so long as it works good and is properly maintained. If you can, handle (and preferably shoot) them both before making a final decision
I hope this helps some & best of luck with your decision.
Kind Regards,
.450Marlin