HSMITH is correct about the heavy loads. However, with light loads (as used in many clay games) it's not much of an issue. I shoot trap year-round, and shoot quite a bit in low light conditions (the lights at the club take forever to charge up).
Anyway, I've got a Browning 425 with factory porting on both (30") barrels. I've never once noticed a problem with flames. In fact, my wife borrowed it for a few rounds, and I watched quite carefully to see if there was any excess flame. There was none. This was all with 1 1/8 oz loaded around 1150 fps.
I did watch a guy with a similar gun "use up" some old hunting loads he'd found in the basement. They were obviously loaded hotter, and he did have some flames kicking out of the ports.
I can't speak too much to the increased noise, as my hearing is already starting to go, so I double up on the protection. Everything sounds pretty mild to me.
IIRC, Angle Porting isn't all that expensive for a single barrel. I even think that they've got some portable (pun?) machinery and can do it on-site at some of the larger events. The other stuff that Dave mentioned would probably end up costing more than the porting (although the felt effects would likely be greater). The stock-fitting would cost a LOT more.