I installed the sear kit myself.My buddy has an Apex in his Shield 9. I shot it and was underwhelmed. I think he just did the trigger though, not the whole drop in kit with the sear. I would consider it in my .45, but I shoot that gun too well to screw with it.
If you decide to install the complete kit yourself id caution to be aware to that you will need to drift the rear sight to replace the striker block that is installed underneath the rear sight. The striker block is under spring tension and it will go flying if you don't drift the sights slowly. The kit comes with a tool to make the swap easier.