I suspect you'll struggle to find meaningful practical experience over in the UK because it's not been around long enough. I don't know if it's any better over your side of the pond, but here I started to notice it probably 3-4yrs ago (although my memory for dates is poor, so it might be longer ?).
The reason I'm sounding so pessimistic on that is because such things like an extra 3-7C running temperature (as claimed by Evans) isn't going to leap out and hit you in the short term. It might not even be a problem long term but at the back of my mind is things like rubber, etc, degrade with operating temperature and hence the service life could reasonably be expected to shorten at higher temperatures. But such details are going to be 5 or more years down the line, not in the first few years and maybe never on a car that's infrequently used.
Anyway, a few guys on the Elan forum tried it and to my knowledge no-one has reported faults, all have said "works well, will use again" which is a guarded positive endorsement.
I can't see any reason why the Evans coolant won't work or deliver the benefits they claim and the only reason I've not had a go myself is that I'm skeptical if the benefits are truly beneficial in looking after my toys. I'm not particularly interested in the novelty of a non-pressurized cooling system, I was looking for comments like "I regularly get 5mpg better mileage" or "I get another 15bhp on the dyno compared with water" but I haven't seen any.
One reference from your side of the pond that I found I'm enclosing just in case you've not seen it. Now I assume this is biased given the sponsorship and the writing style certainly comes across as "their product is junk", but some of the report makes interesting reading.
I was particularly concerned with cylinder head temperatures being higher, which they claimed to have measured and I think, given the nature of the products, could be reasonable. With the difference of expansion coefficients of Steel/CI vs Aluminium I did pause to wonder how long term use would affect head gasket performance ? The temperature data I'd seen before this report concentrated on either removal of localised boiling (which I can't measure/don't know if it's a problem I have) or the bulk coolant temperature rise, which is what you can easily measure although not necessarily what you should be concerned over.
So I'm still on the fence. Here's the report I mentioned in case you've not seen it already. I'd be interested in any references you've found detailing real world gains which are independent of "I'm selling this stuff" bias.
http://www.norosion.com/evanstest.htm (suspected bias but they do have lab reports and "numbers" )
Brian