Funny, I JUST received my NewSouth Performance boost gauge a few minutes ago! I went with the column mount. First off, I figured it will be easier to glance down at when needed rather than glance to the side where the vent-mount is. However, that may just be personal preference as the column is the same spot I had mine mounted in my Subaru before I bought the GTI.
As for blocking, I test fitted and it looks like it will block most of the temperature gauge from my field of view, and as seen above, the tach from 7-8k rpm. All around, it doesn't look like it's going to block as much as that picture above.
Two other impressions: it's big! I was surprised, this is bigger than the boost gauge I had on my Subaru. Not a bad thing necessarily, but a surprise.
Second, it LOOKS GREAT in the interior of the GTI! This looks so much better than the aftermarket I had on the other car. Really, really looks nice in the GTI. The texture and color of the column pod aren't exactly the same as stock, but it goes all the way back to where the column sweeps up into the cluster, so unless someone is really paying attention it pretty much looks stock.
I can't speak for any of the other brands of boost gauge. But first impressions of the NewSouth are good. Now I just need to get it hooked up.
P.S. It's too bad NewSouth doesn't make a brushed aluminum ring as an option to go around the gauge; that would match up nicely with the interior of the MK6.