I have used several TechT products but nothing similar to the hair pin trigger kit.
A-5 with an Apex barrel.
Spider Pilot with progressive barrel.
Reduces trigger pull. Decreases reset time slightly.
Can damage your hammer and sear if you use the wrong sear stop pin.
I played around a lot with the different pins following the instructions given on Tippmannparts.com. I had to play around for a while to get a combination of pins that worked well and also provided the trigger pull I wanted. After I was done I found a combo that worked well for my tastes and worked very efficiently.
Some of the problems I ran into while trying to get my gun to work were 1) the gun going full auto, 2) the sear not releasing the hammer, and 3) not being able to get my safety back into the trigger assembly.
1) If too large of a bottom sear pin is used the gun will go into an artificial full auto because the sear will not catch the hammer. The hammer, therefore, will not reset and will start another cycle. Putting a large bottom sear pin will also create extra stress on the sear and the hammer because it cannot go up far enough to catch on the hammer. I would recommend not going anything over a 3 from the set.
2) When I used the 4 from the hair pin trigger and the 1 for the trigger stop I had a problem with the hammer not releasing at all. The trigger could not make enough contact with the sear and so the hammer would not release every time I pulled the trigger. Like I said, this problem is fixed by using a slightly smaller bottom sear pin.
3) When the trigger stop pin is put in place (either 0 or 1 depending on preference) there was a slight problem with the little piece of the trigger that normally fits perfectly around the safety. Since the trigger does not go all the way forward compared to its normal place the small piece of plastic juts out just slightly. Unfortunately it sticks out just enough not to be able to get the safety back into its proper place. This can be easily solved by taking a file to the small piece of plastic and making it shorter. Doing this will not affect the function of the trigger and is solved in less than 10 seconds using a coarse file or sandpaper.
After finding the proper pins to use and my preference for trigger pull I was very pleased with the hair pin trigger. for those interested I use the 1 for the trigger stop and a 3 for the bottom sear pin.
The hair pin trigger does exactly what it says it will. Since every gun is slightly different some people may be able to get away with using different pins and get different results with each. This upgrade does require a bit of work but I was able to test many different configurations of pins with many different results giving a broad range able to suit many individual preferences.
I do not regret buying this upgrade at all. It was worth the $20 I spent for it. I have to lower the rating only slightly to a 9 because it requires some tinkering to get it to work properly.