As much as a class action law suit is there for a reason, it seems rather pointless to those that are supposed to win in the end. Since you are going to be receiving $40, that doesn't even cover one month at the 5GB ($50) plan. I should think since they brought this new plan in to affect two months in, you should get at least 2 full free months ($100). If you are going to make a class action suit then why wouldn't you go for what is actually fair?
http://www.macrumors.com/2013/10/30/original-ipad-3g-customers-begin-receiving-claim-forms-for-appleatt-data-plan-settlement/