When P6s were cheap I didn't really get the point when you could have the real thing and get it refinished if you wanted.. Now that P6s have shot up in price and p225a1s are hitting the used market, the A1 makes sense because of the updated features and the p239-like design, and the p239 by now is a proven pistol.
Everyone put it perfectly, the p225/P6 feels like it was made for your hand, the p225a1 retains this same feel and balance, though slightly heavier and so on.
As someone who has carried basically every model Sig, old and new, the big downside to the p229 is the weight and thickness when compared to almost everything else. It's my least favorite classic Sig. The original ones in .40/.357 Sig are pretty good, but the p228 blows it away, the p226 blows it away, the p220 blows it away....The p225, p239, p224 all carry easier. Just my opinion.