With LTLX7000 being out, the main question asked of most shotguns is "are they as good as LTLX?" As for M26-MASS, she does her damn best trying to be. While LTLX has her SUPER dumb damage mitigation in her active skill, M26 has it baked in as a passive. If any damage she takes is 5 or lower, it’s completely ignored, as if she had very good flash rounds. This is applied AFTER armor mitigation AND flash rounds. With flash rounds, she’s essentially immune to anything 8 damage or lower, which is very strong. However, if the enemy does too much damage, this passive does nothing. However, in current day, LS26 exists. This fixes damage taken to 5 which, spoiler, is negated by MASS's skill. Can be very strong to force MASS to tank some insane things. How often will that be used? Eh. It's neat at least.

The one thing she does have going for her with her passive is that she can actually mitigate damage that bypasses armor. You can entirely mitigate stuff like grenades through it. You could sit in gundam range for a bit and not fussed about it. You could even sit in Typhon lasers and be fine. (Depending on firepower of Typhon, please do not attempt without consulting a local doctor)

Overall, she does fall short of LTLX just due to the sheer power of doubling your armor along with 20% DR. The utility of her active also is less relevant compared to LTLX. Removing HP shields and buffs (which get far more common) is stronger than a Molotov and DR to backline. To add to that, the 6 second initial cooldown hampers the effectiveness of the backline portion of the skill. This is because most things that do target the backline would already be skullfucking you at that point. Other cases this is bad include maps M26 shouldn’t be brought to for one reason or another, like when shotguns are bad for it in general or you can’t use machine guns.

G&K's equal opportunity things means even penguins are accepted, I guess. She has a finnicky, slow, and generally not reliable shield. On the other hand, her gimmick relies on having shields.

She relies quite heavily on outside shields if you want to use her gimmick, so stuff like SAT8 and LWMMG mod will come in handy if you want to do so.

However, while she has good armour, her HP is the worst of the 5 star shotguns, and she doesn't have particularly good tanking gimmicks. She's usable, but probably wont be your first choice unless you want to use her gimmick that badly for whatever fucking reason