I cant comment on the Leon but i fitted a carbonio to my mk1 octy vrs....went to one of them rolling road days at impossible performance in kent and i had two runs...1st run stock...car produced 179bhp...2nd run with carbonio...car produced 187bhp....this was my first mod on that car and after that i added a few more bits and got it upto 230bhp with the same tuners......the carbonio i thought was a great bit of kit and the sound was good..not intrusive like a K&N for example but the noise from the wastegate going ssssshhhhhhhh up the carbonio was awesome...pick up was instanlty improved too...get one!