I've never sent one out to CGW or CZ Custom. Bought their parts and installed them myself.
But, and it's a big BUT, installing the parts is only part of a job. They are the guys with experience to notice something not quite right with the other parts in your pistol that their parts have to work with. They are the ones who know if a part just needs massaged, or if it needs to be replaced. A job they do should be better than a job most of us can do. Can we get close? Sure. Some of us closer than others. Also, if you send it to them, keep all the paperwork in the box and then at some point decide to sell it, it's worth more with the proof of what parts went into it and who did the work.
So keep in mind what you want so you'll be happy with the pistol you end up with. I have Omega P01s (cocked and locked, cocked and locked) and they feel really good in my hand and shoot darned good, too.