Looks a baragin to me!

Ceramic Heater at Maplins

You could buy a small bank of them and sort most problems with them. Especially at that price.

I've got one of those,sadly i think i need another 9 to clear the screen

I think I breathe out more hot air than it does

sad fact of those is that, with a 15amp fuse and running at 12v, it can only put out a max of 180watts - which isnt much as heaters go. In fact thats the curse of 12v in general, trying to deliver a nice amount of power without using stupid amounts of current.

Double trouble is that its an open car and any warm air will blow away!

Much more efficient to plumb in a heater matrix and use the engines heat.

All that said though, would an SVA man count this as suitable demisting and pass it? If so, i suppose its all good, just dont expect amazing results in reality!

Surely much easier to just get it tested without the windscreen fitted in fact.

There are legislatory standards the OEMs must meet for demist performance. I'm working on the new mini and we are using HVAC systems with PTC (Positive Temperature Coefficient) units. These are 12v and are rated at 900 watts - they are used on Diesels because they take too long to warm up. I've got a couple I'm going to have a play with; trouble is they are not cheap. The other thing you'll find is that demisting is more about having a blast of air as much as it is about warmth.