It says it will cut metal; does that include mild steel and stainless?
I need to cut a 2 1/8" hole in a steel door for mounting a deadbolt.
Actually, it's a hollow core wooden door that someone laminated on both
sides with steel sheet (I think it might be stainless.) Is it worth a
try for $20?

Or should I just drill a bunch of 3/32" holes, knock it out with a cold
chisel, and clean it up with a half-round file? I assume I'll have to
do some filing if I use the oscillating multitool, but not a lot.

The hole saw I bought didn't do much except draw a circle for me and
make a pilot hole.

Let's say it doesn't work for this. Is it worth $20 anyway? Thanks.

-Bob