I have to echo what Caribou said... why do you want to trade? Make a list of reasons it would be a good trade, make a list of reasons why it wouldn't. Personally, I own Glock, XD, S&W, and Sig. Everyone of my handguns I love for different reasons. If you plan on using it concealed, a G22 even though the specs say about 1/2 inch bigger than the G23, is much harder to conceal. Is the M&P 40 the compact model, full size? These would be questions I'd be asking myself if I were thinking of the trade. Is the other guy willing to let you shoot it first? If so, take him up on the offer.