Hello,
I'd rate them as the best value for money... If you are looking at the Vecton units then the V2's have a better hosetail attachment method (a threaded collar allows the pipe and hosetail to be removed from the unit more easily than with the V1).
The old argument... "are they needed?"... hmm... I use them, I rate them highly and I personally would recommend them.
I'm happy with "that little bit extra" peace of mind that they provide me.
I would say to anyone... do your own research and make up your own mind. I would recommend that anyone ignore any manufacturers blurb (a profit to be made!) and talk to people who actually use these devices.
Bodge99