Are these good for handling sheet metal?

Yes. They are cut-resistant goatskin gloves, so they suit sharp-edged sheet metal, glass and similar material. Goatskin is soft and grippy, though it abrades faster than cowhide on rough edges.

How do they compare with coated cut-resistant gloves?

Leather gives better feel and grip on dry material and holds up to light abrasion. Coated knit gloves breathe better and stay flexible when wet, but leather is usually preferred for grip on sharp, oily parts.

Will the leather stiffen if it gets wet?

Yes. Goatskin soaks up water and hardens as it dries. Let them dry away from direct heat and work the leather to keep it supple.

Do they protect against punctures?

The stated protection is cut resistance only. There is no puncture or impact rating given, so do not rely on them for needles, wire or struck-hand hazards.