Re: nightmares having guitar built!!!!
Not wishing to pass comment on any of the people in your list, but I think that it is pretty unusual for anyone to have a custom made and not find a single issue.
The fact is that you are asking an individual to make you a one off, and that rarely goes without any issues. Also people tend to forget that factory made guitars have issues as well, but the finish often covers this up, or they don't really check that carefully.
I haven't seen the work of any of these guys in person, but I have communicated with Jaden and he seems like a straight forward bloke.
The fret work issue doesn't sound great, and 1mm is quite a bit, but I have seen 0.5mm difference on some factory made guitars. I am not defending that, but it does happen. To be honest for £600, that is unacceptable, but for that kind of money the neck would have to be unbelievably good just to justify the price tag.
My question to you is: if you are not happy with the work the luthier has done, how have you ended up with 4 of their guitars? Surely if the first one is bad, then you don't buy again?
All I can say is that I hope you got your moeny back on the necks!