They seem to be quite popular in the UK. Have no extensive personal experience, used a couple on rifles belonging to friends and they seemed to be an excellent piece of kit.
I know of 3 mounted to a .243 which has been very heavily used, a .300 win Mag and a .375 H & H Mannlicher. Can't say how heavily used the .300 and .375 are, but Bill, the owner, seems quite pleased with them.
The one on the .243 has seen some of the worst of the scottish weather and been knocked about considerably in the back of land rovers etc. Although marked and scratched on the body, it has performed flawlessly. I used it to test some loads and even though it was well used, the adjustments were positive and the optics, clear and bright. From what I can see, they are very good value for money.