You would probably get more replies if you posted it in the Ibiza section - but that is just a guess, I just don't want to think about doing that to my wife's Polo as its okay as it is, insurance company might need more money as well.
So far that engine does seem to be reliable with not many people complaining about it, so why not just do it?
I had a remap on my Skoda Fabia 1.2TSI and since the engine is the same my experiences below should apply for the Leon as well.
Even if the figures aren't super impressive for the gains I was very pleased with the added grunt after the remap on my Fabia. Mine had 131HP/234Nm if I recall correctly and especially the added torque made a huge difference in driveability with the manual gearbox.
Pros are more go, better driveability across the rev range, less need for shifting (on a manual) with no noticeable increase in fuel consumption on normal daily driving.
Cons are the same as on any performance modification i.e. loss of warranty, more stress on the engine and drivetrain which might affect the longevity, regular servicing is a must etc. This is always the risk you need to be ready to accept when modifying a factory car.