Dean, I also looked at that aquasoil. I think Alistair said he'd a mate who used it and it was actually quite mushy (probably not what you want lol).
I've gone through the same debate over and over on what to use, at the end of the day you have to get what makes you confident that you can try to do well in it. We know plants can be grown in inert substrate if dosing properly, but most folk use a planting substrate.
I always think of my days fitting TV aerials and delivering electrical goods, people would spend £000's on latest TV's etc and when we installed it the picture would be crap and we'd say you could do with a new aerial that would cost them £60/£70, the amount of people who declined through not wanting to spend the extra, amazing... lol
. Liken that to the aquarium, tanks cost, filters cost, lighting costs, etc etc so when a substrate is a £10 cheaper than a proven well reviewed one you may leave yourself wondering about it which isn't a good place to be. I spunked £100 on 30L of the columbo stuff which is big gulp, but in the scheme of things i'm confident it will look how I want and provide everything I need to do what I want. The extra money is worth the peace of mind to me.
This is, of course, all just my novice opinion on these matters