So long as it matches your year it shouldn't make any difference. But best thing to do is to message the seller really. They'd know whether it would fit or not.
I don't know about stock pipe but I'd say so. But might want to wait for a definitive answer.
If this were me I'd say the extra £30 and buy the DEP end can.
Well, I ordered and got athena silencer. It perfectly fits original expansion chamber without any modification. Here is picture of it. And thank you guys on your help!