TLDR: once it is installed and set, it is great and it is worth the investment. Problem is there is no manual nor guidance, and I think a Guns Modify complete spring set is also needed along with threadlock, time and patience.

In my opinion the GM trigger set is the most sophisticated and best engineered airsoft aftermarket parts I have ever seen. But installing it is a massive PITA. Be prepared with time, threadlock and an extra GM trigger box spring set. In my sole experience the GM springs are somewhat stronger than stock and work better. There is no guide and that is what makes the install a lot more difficult than it should be.
The trigger is fully adjustable and my recommendation is to find the sear engagement (pre-travel) setting first, that is at the front of the trigger and set from the topside, not the bottom. Start adjusting until the disconnector can no longer release the hammer, dial back a bit till it works again. Assemble the trigger box with the fire selector and start adjusting the reset (at the end of the trigger, can be adjusted from the top) until the selector no longer works, as that is a limiting factor. Half or quarter turns. I set mine up in single stage mode so I cannot comment on the two stage one. Trigger now feels great and resembles a real AR-15. I am satisfied with the product, I just wish GM took the effort to make a guide so I could have saved the time it took to figure out everything myself.