Your friend no doubt thinks your 625 is a better gun or he wouldn't be wanting to trade his Sig for it. I agree with let him sell his Sig and then go buy a 625 of his own.

I have a 9 and a 40 Sig P226 and I wouldn't trade them for any S&W auto. S&W has their good points and so does Sig. No point in comparing apples to oranges { revolvers to semi autos} so to speak.