Id go genuine from VW... theyre only cheap just a brake light switch. DIY fit... I think its one of those switches that getting aftermarket may not be the best solution... Your call though

i know on my mk4 ibiza they had made changes to the switches so it was best to get one from the dealers. The one i took out was completely different to the new one, solved the faults and i never had an issue again.
Saying that though! A couple of years later i had the coil and traction control lights on the dash and it was because both brake light bulbs had gone... problem solved

... just a thought.