Long time lurker here. I have now got the GFB DV+ as the guys from GFB were at the shop when I was there
I got it fitted at JD Engineering in the Netherlands. The rolling road comparison showed a marginal increase in torque of a few N/m.
What is more important to me is reducing leakage. I had the latest plastic piston type valve in my car. They fitted my valve to a alloy block they had made up to check valve leakage. I wasn't aware that it leaked so much. Taking the piston apart I suppose I should have known. The plastic 'sealing ring' seems to have at least a mm tolerance. The guy from JD engineering said it was like having a 6mm hole in the intercooler.
So while power might be marginal (but measurable) what was more important to me was leak reduction which will reduce turbo rotational speed and therefore reduce heat.
Well, put it this way, if you had a small intercooler leak, you would fix it. So why not fix the diverter valve leak? The GFB parts has life long warranty, so it was a no-brainer for me...