I have not been able to personally test the Act Labs guns, however I have had a lot of feedback from people who have. So lets see if I can answer your questions:
1. Define "well". They work. They have hardware flashing so they work accuratly, at least on most displays. Very little that you can customize about them. The second part of this question is a matter of opinion, obviously I think they arn't worth the price - but depending on your setup they may very well be easier for you.
2. Yes, to my understanding the video is passed through. Even if it wasn't, splitters arn't expensive.
3. Yes. Onscreen shots are always mapped to Left Click, and offscreen shots are always mapped to Right Click.
The Guncon2's use RCA out, worth noting. As for Guncon2 or Act Labs? Act Labs can probably give you commercial support, where you only have community for the Guncon2's. Act Labs guns give you 100x less options and customizability. Act Labs are MUCH more expensive, but might be easier to set up.
Hope that helps some, let me know if you have any questions.