I use one, and it is easily the easiest wheel lock to fit, and seems as secure as any other and better than some. It has Sold Secure gold standard so has passed the tests to qualify and I get a small discount on my insurance for fitting it.
Having said that if you are fitting two wheel clamps, I would use two different ones which might just make life that bit more difficult for potential thieves. basically if they can get the clamp of one side then they can get it off the other so give them a second problem to solve.
I have always used the Alko, however changing my can this week to a longer one doesnt give me enough tolerance on the drive to mess around with the Alko, and I too have gone for the Nemesis. Incredibly easy to fit and seems almost as secure as the Alko. Combined with an Alko hitchlock I have no security worries.
The Nemesis is well packaged, seems robust and secure. It takes a few minutes extra to initially setup, but once done it has made my life so much easier.
I am also intending to add locks to the steadies for when the caravan is on my drive.
I use one of these devices when I am touring,They are relatively easy to fit ,but as with everything else, if they want it nothing will stop them. No point in worrying yourself into an early grave, just make sure you are well covered by insurance.