One of the units I'm thinking of including in my Squat 'counts-as' Imperial Guard army are Psyker Battle Squads, possibly two units of 6-7 each. I've seen them used to devastating effect against some armies, however I am unsure how well they perform against loyalist Marines, bearing in mind they automatically rally the following turn with their ATSKNF special rule.
Have you used Psyker Battle Squads against Marines? Or had them used against you? Opinions and thoughts gratefully received!