In reality it should be something to do with what you use the car for. If you autox or track the car then sways or a trackday. If you drag then I'd suggest something else, maybe a kartboy short shifter. If it's a daily driver then perhaps i'd suggest mudflaps.
Tell us what you want to do with the car in the future/what you do with the car now?
If you already have a protuned STi I would put the $250 into a bank and save up for a major mod. Think of it as the begining of a turbo and front mount fund. Dont waste money on unnecesary parts. Save it for those parts proven to make a large difference.