You clearly are a tinkerer of the highest note. So, let's see the Chinese jig cost you about £80. The material for the rest of your setup is probably somewhere between £50 - £100. And then I reckon you spent at least 10 hours building that rig, which in my book is equal to no less than £200. In my estimate this means you've already spent more than if you were to buy the Granberg mill. Although, admittedly you probably had more fun.
And then you claim that if you hadn't used that jig, you would have "butchered" the wood. Well, I have two chainsaws, and I have cut up a fair few trees by now. Some of them in excess of 3ft diameter, and I can tell you that with a little bit of experience, and a nice sharp chain, you can get a very decent straight clean cut without any jig whatsoever, just free hand. It does get a little tricky if the trunk in question is more than about 6ft long, but I don't get many of those anyway.
So overall, I think you had some good fun and the results are worthwhile (although you might want to try a skip-tooth chain, tends to work better on these rip cuts), but efficient it is not.