Your choice mate. If you really think a ebay plug in tuning box will make as good difference as a remap from the likes of R-tech, badger 5 etc then feel free. Im sure anyone on here will be more than pleased to see a map as good as theirs for 1/4 of the price delivering the same SAFE results. Post the rolling road results up / logs of sensors and sure you will have majority of the VAG world interested IF they do a good job. Compare them to the likes of the big names and see where it stands.
I can guarantee, that 99% of the people you will talk to...would recommend a proper remap.
Sounds like your AGU if your going for k03s and FMIC....you do know a K03s on a AGU engine code requires a custom remap dont you? There is NO 'off the shelf' map available.