Well a couple years ago I had the zex system on my car. I started with the 100 shot and it was very reliable. I ran Ht0 plugs and turned mid 12's @ 110 with an auto. Never lost a plug on this setting, but I was running the HT0, not the HT1. Tune was a mail order Brenspeed tune. Then after a short while, I got it dynotuned with the 100. I saw on the dynotune that the nitrous pressure makes a big difference. Huge difference between 900 and 1100 psi.
I went up the the 125 shot, but I would loose a plug from time to time if I ran full 1/4 mile passes on pump gas. Not a problem 1/8th mile. I backed off the timing a couple more degrees and ran 100 octane and didn't loose any more plugs as long as I did that. On the 125 I was low 12's, 12.1X to 12.3X.
Then I added a BAP and went up to the 150 shot. The car eventually went a 7.38 1/8th mile (which is around 11.60 or so), but when I ran the 150, in addition to running the HT0 plugs, I also gapped them down to .035. This was not needed on the 125.
In addition, I had a bottle heater, a nitrous pressure gauge, I routed a purge kit which emptied out the front grill. I kept the n20 pressure around 1050. I also had two bottles in the trunk so I could run all day at the track and not have to worry about loosing bottle pressure.
I did, in fact override the TPS switch activation with the zex kit, not because I wanted to, because I had to. After a while, the wire from the zex box to the TPS was causing the car to throw codes. I took this wire off, and in addition to the arming switch which I had in the center console, I mounted the activation switch right by the shifter. This worked because I had an auto---the location of this switch will require more thought with a manual.
However, I don't know if I would do this again---just letting you know it is possible. Having the system activate off of the TPS in conjunction with the window switch would be best. Zex.com has a window switch under accessories.