What they describe will clearly work. What they don't mention are some of the other effects.

The autospeed site (which is actually quite cool) was trying to keep cost down using std of the shelf pneumatic components from Norgren. (BTW, any manufacturer of this stuff eg SMC, Festo, CKD etc. will do - it's all the same). I find it a little crude to take it offline from the ECU as the safety mechanisms are bypassed as a consequence. For instance, if the ECU detects pre-ignition through low octane, it can still retard the ignition but cannot reduce boost...

Presumably the Audi's blow off system can still cope with increased compressor surge as a result of the wastegate becoming on/off in its action. Something to consider however whenever modifying wastegate behaviour.

In this day and age, professionally reprogramming the ECU or replacing with a Motec etc. has got to be a better option. Their solution is cheap and cheerful though (well, at least until something goes wrong...)