Overview
RMB-93’s Mod gives her a nearly usable tile layout, an extra point of base armor, slightly not as horrible base HP, a damage amp debuff on skill 1, and more knockback. Also 3 extra move speed and a point of armor on her mod SPEQ.
Those are mostly irrelevant though, as the main draw of RMB-93 Mod is her skill 2. She takes 4 less damage each time someone else reloads. This stacks up to 3 times. With the recent release of a bunch of flat damage reduction units, RMB-93 Mod is pretty close to taking the cake.
By joining her with another unit that reloads very often (Defender recommended, Dana Zane otherwise), RMB-93 Mod can maintain -12 damage taken from all sources. Permanently. This makes for really high effective armor and lets her ignore a few weaker armor ignoring attacks. This stacks with the flash ammunition to make a grand total of -15 damage.
Mod 2 is definitely a game changer, but Mod 3 can be occasionally helpful as well with the Mod SPEQ.