Sun Lizard: any good?

Sun Lizard system diagram

We've been getting quotes for heating in our house, as it's starting to get cold. Initially we thought we'd go for a flued, fan-forced gas heater in the fireplace in the lounge room. A friend has the unflued gas heater recommended by Choice and it's brilliant. Heats her whole house really well. We figured flued because then the exhaust gases go outside.

Turns out gas heaters of this calibre, flued or unflued, are around $3,000 or more plus installation. Not cheap! So we decided to have a look at ducted heating, which if it comes in at under double that, I reckon isn't a bad deal since it would heat the whole house.

Now I've found The Sun Lizard which was featured on New Inventors. It uses heat from the sun to force warm air in or out of the house, depending on the season, and stores the heat in the thermal mass of the house. Given we're in a double-brick house, we've got plenty of thermal mass.

This claims to heat by 4-6° which sounds like it'd probably be enough most of the time for us. In addition, it cools by up to 10° in summer which would be a nice bonus. At under $3,000 it sounds like a nice option, and with no ongoing costs it's quite attractive.

But I'm not sure 4-6° is quite enough, even in Sydney's mild winters. I vowed when we bought a house to never spend another winter shivering with all my clothes on and a crappy electric heater sucking down expensive juice. This is the experience of poorly insulated, unheated rental properties for about a month a year in Sydney.

I wonder if the money we were thinking of spending on ducted heating might be better spent on a unit like this and upgrading our insulation. Get the roof vacuumed and the old insulation replaced with modern, high-spec insulation. As an added benefit, it would reduce plane noise. We're also looking into double glazing, which has benefits for both thermal and acoustic insulation. Perhaps with greatly-enhanced insulation and this unit, we could get by with a crappy electric heater used for only a few days a year?

So does anyone out there have any experience with this unit?