I've used essex arms as basis to build several full custom 1911s, The thing to remember is it takes a pro to build a full custom from a bare frame/slide considering that it takes years of experience to be able to extract the most from handfitting and componet selection. After being at it for a good while,you'll learn to do it by feel that no book can teach you.
I work in the town where Essex Arms is located. I have seen their stuff and their facility and would say it is a little above "acceptable", but it's certainly of much better quality than RIA. My opinion.