My generation ship aliens have 2 thumbed hands. No, not the 2 thumbs on the same side that some humans have but the 2 thumbs on opposite sides. So it would be kind of like this:
Except more reptilian and less human as far as the skin but this picture right here is of a hand with 2 thumbs and the thumbs on opposite sides of the hand.
The reason my aliens have 2 thumbs on each hand is to increase their grip strength. The grip strength of the pinky may be 50% of the total grip strength of the human hand but we wouldn't have much grip strength without a thumb. Having a thumb makes us better at grabbing on to things. I would imagine that having 2 thumbs would be even better. Plus, with a 2 thumbed hand you could cross your 2 thumbs while having the other 4 fingers relaxed. And counting in base 12 would be easier too.
Anyway, would having a second thumb on the opposite side of the hand increase the aliens grip strength significantly? I think it would, but would my aliens really have significantly better grip strength than humans with a second thumb on the opposite side of both hands?