the main thing is you get a matched key and box, this can then be matched to your ecu with vag-com. doesnt even have to be an abf set, any mk3/seat one of the correct era will do.
matchign a new key to a transponder box reequires an skc code, which you cant get any more, so this is a dealer only job. however vag-tacho can sometimes be used to retrieve the skc, but afaik this can only be done if you already have a matched key in the ign lock.