I saw that thread myself - but not much else about them. That said I did get a chat with a local established installer and the prices really have tumbled since I looked at this a few years back and in fact his ball park figures weren't much more than those DIY kit prices (for a full 4kw install)
The DIY route i guess allows for a small cheap entry point then you can add panels later.
Then it's up to you which route you want to take.
But please be aware if you are going to install the kit yourself, and it involves tinkering with the household electrical installation, you will need an Electrical Installation Certificate for insurance purposes.
The diy route would need to be alot cheaper I think. Ultimately 4kW is what I need to aim for and if there's not much difference in price for a 4kW then the hassle of diy is hard to justify.