I would use them regardless, I've only used plastic, don't know about the metal ones.

If you are asking, “will I damage my gun”, it depends on the age, make and model. Most modern firearms (all the big names Colt, Glock, Smith, Steyer, Sig, HK, Taurus) can be dry fired without damaging the gun.

I want to get some Pachmyer red snap caps. I want them for malfunction clearance drills (having owned a Kimber I am quite adroit at clearing jams) and mag change practice.

Make sure to follow all safety rules for dry fire practice.

A good use for Snap Caps is a training and teaching aid.

You have someone else load your mag and insert one snap cap at a unknown postion in the mag to the shooter.
Then the 2nd person can watch your trigger control and the shooters recoil reaction, as the snap cap didn’t fire. The shooter can also see he maybe anticipating the fire of the gun as he may jerk the gun even though it didn’t fire.

I may not have worded this to well but maybe it can be understood.

I am a believer in Snap Caps. I keep them in all my handguns during storage and use them every evening for dry fire/malfunction clearing practice/Mag reload practice. I know most all modern firearms manufacturers state that the weapons may be dry fired without damage, but I will never forget the 9mm Star I purchased at a deal 30+ years ago that I made the mistake of dry firing and on the second snap saw the end of the firing pin exit the barrel. Stupid kid new to law enforcement and handguns. Took 2 weeks to get a gunsmith to make another. I practice because I carry and snap caps buy me peace of mind. They also feed like most ball ammo and the Pachmayr have a brass "primer" that is spring loaded to absorb the force of the firing pin. It lets me check my tactile ability with loaded chamber indicators on my Berettas without changing my grip as I would with a live round as well. Practive everything and you will be reduced to your personal level of training when the crunch comes.