1) Have not use before. Basically Techron is a fuel additive that helps to keep clean burning environment, given correct ignition timing and right amount of air/fuel ratio, hence keeping your combustion chamber from deposits formation.
http://en.wikipedia.org/wiki/Techron
http://www.techron.com/what-does-it-do/default.aspx#
Internet information mostly are free to obtain. Gunalah Google, jgn tak guna
2) Decarbonize means to blast off the deposited carbon in the engine. Techron is NOT A FUEL CLEANER, it helps to keep your combustion at optimum cleanliness. Change of fuel filter in a regular manner is more feasible in my opinion, rather than keep pouring additive in the hope the fuel system become clean.
3) Basically, Techron changes the fuel characteristics by molecule. So, it doesn't harm your car given the correct mixture is properly measured. If you're scared of gasket leak, why not start with CALTEX petrol
4) Doesn't really matter when you change your engine oil. As long your fuel tank is close to depletion, drive to your nearby petrol station, pour in the TCP and fill up petrol to the brim and start driving.

Trust me, you will feel absolutely nothing after spent on the TCP, however if your butt is sensitive, you will feel a very smooth pickup, feels more powerful, feel more torque and probably save some 10~20km/tank of petrol

haha. well said bro.

kena setepek. some said u fill up caltex already have techron. haha.

next time buy octane booster or ceratec better.