Sorry but i'm kinda re-educating myself about this game....

According to my old companion rulebook they are not compatible. Does that mean you cant get both or you cant use both at the same time? Like can a character get both and just select which power he uses at an applicable time or he cant buy both on one character?

I would assume the latter. I doubt a person who has this edge is flat-out prohibited from buying the combat sense power. I'd say an adept with both can choose to either get his LR dice for free, or to add some fraction of his combat pool to the surprise test, but could not add dice from both sources. Assuming the fraction of your combat pool you can use for surprise tests is larger than your LR bonus, then it's a viable option to have both.

I don't see a particularly strong reason why it would be SOOOO broken to let them stack, though. If you want to make a "quick-draw" adept and stack combat sense on lightning reflexes, I think that sounds like a fun combination. Sure, you'll dominate surprise tests, even when ambushed, but it still doesn't seem that bad.