How to reset ECU?

And this is a good thing to do after a modification right?

It can't hurt. It forces the ECU to immediately re-learn the fuel trims, rather than adapting slowly over time.

The general concensus is that CAIs on a WRX are not really worth it, though. They both increase the likelihood of ingesting water from a puddle (minor risk), and lean out the intake mix by throwing off the calibration of the factory MAF sensor (typically a minor issue if that's your only mod). They may make a small amount of power by leaning it out, though.

Just disconnect the negative batt cable and press the brake pedal down for ten seconds. If your clock and radio stations are cleared, you're done.

Always. And when you first start the car after reconnecting the battery/fuse/fusable link, put the key in the "on" position for a few seconds without touching the gas. Then start and let the ECU re-learn the settings with the new mod. You can spend that time resetting your clock and radio presets.

That is true, one of the tuners on

Only 3 manufacturers (APS, Perrin & TurboXS) actually make a CAI that they guarantee won't interfere w/ the MAF. The only one of the 3 that I've found to be exceptionally made is the APS unit. Perrin is probably my second fave of them w/ TXS coming in 3rd, although none of them are "bad" CAI's.

TXS's isn't a CAI, though - it's a short-ram intake (just a pipe, same diameter as factory, and a K&N cone filter). I have one, and love the sound. No complaints with quality. Have heard good things about APS and Perrin as well, though.