In the August CC Magazine there's a picture of 2 Alko Locks that have been gas-axed off.
Sold Secure don't test for removal by this method yet any self-respecting pro thief will have this equipment. The "Diamond" category is nothing more than a marketing ploy in my opinion.
I got these (I need 2 for my twin axle).
http://www.jsbhublock.co.uk/indexhtml.html
I'd say they are less awkward to fit than an Alko lock but take slightly longer as you have to jack up the van, take a wheel off and put this on. Because of this it is not a replacement for a wheel clamp but for use when on site or in storage I don't find it too bad. I'd rather not have to do it - but the reality is that if you want to keep the 'van you have to make these efforts!
I believe they are much more of a deterent than the Alko type hub-locks (and the bulldog version). They say it is not possible to remove them without fusing the hub and making the van unmovable. It could still be loaded onto a flat-bed and driven away so it isn't infallible, but nothing is.
Bottom line is that security is a trade off with convenience. Everybody needs to make their own informed choice. "Sold Secure" is a tool to allow purchasers to make an informed choice. Just be sure to read the small print.
Oh - and for the record, I don't have any connection with the hub-lock other than having bought a couple. I just think it's worth serious consideration by fellow caravanners dazzelled by all the "Sold Secure" shiney stuff out there!