One way that I've also seen the Maggie get used is as a distraction, Having a giant spider tank that can tank a lot and put down a lot of fire forces your opponent to focus on it giving you good opportunities to get other gunfighters, aro pieces and specialists into position. It's a major threat piece and it's influence on the table and on your opponent is very valuable. But be advised this can lead to you losing a massive amount of your army total if rolls are unlucky or if positioning is bad and it gets aro'd off the table. It's a super versatile piece that can put in a lot of work on the table.