I have only used this tool for thick aluminium but it has worked really well having a very narrow point has also helped as I have been enlarging pre cut slots from 6mm to 14mm to me it is worth every penny
Bought this step drill to drill 20mm dia hole in my car boot and metal plate, as part of tow bar fitment (approx. 1mm gauge metal). First drilled a pilot hole with a HSS twist drill then used the step drill to open it out. Fantastic control taking it up step by step leaving a very clean circular hole with no burs. No pressure required just allowed weight of drill to take it through. No signs of wear/damage to step drill, it was one of the cheapest I could find and will last a long time.