Here are some updated:
First, I had another client who wanted me to upgrade his gun with RA-Tech steel trigger components. I compared the trigger box and the RA-Tech was machined exactly the same as the stock box. However, the RA-Tech hammer was slightly higher as shown in the picture below. Although the height difference is minimal, the implications are significant especially when you use the RA-Tech steel bolt (the lower surface wasn't machine exactly to spec with the stock WE M4 open bolt)
I installed the RA-Tech trigger pack and the RA-Tech steel bolt without modifying the underside. I can still pull the bolt but I can feel resistance immediately when the bolt attempts to cock the hammer. I grinded the underside of the bolt and that fixed everything. I can now pull the bolt via the charging handle with no resistance at all.
Second, if you are using a RS fire selector (which i highly suggest as they are more durable and stiff so it doesnt wobble), I recommend the CWI trigger set. If you want to continue to use your stock WE M4 fire selector, I think the RA-Tech trigger set should be fine, just dont modify the trigger set. Ive only tested this for a brief time, so Im not sure how it will perform in the long run. Needs more stress testing.
These are my preliminary thoughts..