I thought they were just a gimmic (and I guess they pretty much are) but a buddy of mine had two 4.5-14x50 and when compaired to my 4.5-14x40 it blew it away in low light. I'm not a fan of a large objective lens because of how high they need to be mounted. He had basically the same set up mount wise with beter performance. I bought one of the 6.5-20x56 VXL's and it's a great LR low light scope. I still had to put a cheek piece on to get a proper sight picture. With my 20moa rail I have enough adjustments to have a 100yard zero and get out to about 1900yards. The only thing I don't like about it is the VH reticle and wanted a TMR, but you can't get the reticles in the VXL changed.
They were upgraded with the dual spring erectors and better lens coatings in 2009 along with the VX3. They make for a sleek looking gun with a sporter stock but with the higher straight combs many guys are shooting on their long range rigs, the cut-out isn't a big plus since the comfortable scope height is usually high enough to clear a regular 50mm.
They are wider than a regular 50mm to achieve the same amount of lens area.