In wood, it went great, but in 5mm polyester, from the second cut, it found sticks, I wouldn't dare with iron at all

Personally, it saved my face. I opened 5 holes in a thin sheet metal of a computer tower to install extra fans, and I can see that it will withstand many more in the future. For such tasks, I recommend and suggest low speeds and the use of oil for drilling. I recommend it.

The purpose of the purchase was to open 2 holes in the Computer case in order to install 120mm fans. It did its job perfectly. I used a rechargeable drill at low speeds and lubricating oil for a chainsaw that I have for cutting. Then, I did some fine sanding with a dremel to smooth the edges. It worked perfectly. That was the purpose for which I bought it. The case metal is thin. I cannot express an opinion for thicker metals. It doesn't seem to have suffered any damage, so it will be used again in the future. I recommend it for such tasks. I don't think there is a need to go for more expensive and specialized hole saws with much higher cost.