Yeah the 1.8T side mounts were literally made for standard boost and no more. The TFSI front mounts can cope a lot better with the boost turned up.
Yep, short boost pipes = much more responsive!
That Merc one is a air-water though (aka 'chargecooler'), which is much better at cooling than air-air, hence it's tiny size.
Probably something I would do if going big turbo but with K03/K04 any of the aftermarket front mounts should be fine. Is the Audi one worth it as I keep hearing it's only a tiny bit bigger than the Golf's?