2 flutes tend to have better chip capacity, so it lends itself to heavier cuts. On harder materials the cuts will be far less, so the feed must be reduced since it has half the number of teeth. So it will work just fine, it’s just less effective.

I prefer carbide for harder steels and non-cosmetic work. HSS is nice for softer materials and for the best surface finish. I have a few razor sharp mills I keep for delicate work.

What you read about 2-flute cutters and softer metals is more applicable to modern cutters that are made specifically for aluminium. Due to the higher cutting speeds and higher chip loads that can be used on aluminium the amount of swarf produced can be quite high. The deeper gaps between the two cutting edges can better handle the removal of these high amounts of swarf. They also tend to have a higher helix angle to lift the swarf out of pockets faster than the traditional 30deg or so found on cutters like you have.

The sizes we see on here ,in the main tend to use various types of collet holder but older machines eg the centecs used 2MT. Carbide and inserts can’t easily be sharpened where as a HSS cutter can and an MT cutter keeps things nice and close to the spindle. I have several ! Noel

Don’t clean hss with a sand blaster unless you have the facility to re-sharpen them.

I thought the OP was talking about sandblasting the milling cutters?

Rob