Friend, you will get different opinions from different members. I personally have never seen a snap cap. I have over a dozen shotguns that vary in age from 6 months to 50 years. I always snap my guns when I put them away after use. Never had a broken firing pin.
I have a friend that takes pencil erasers and inserts them in the primer pockets of fired shells and uses this, He has never had a broken pin either.
I wouldn't waste the money for snap caps. However, it is up to you to make that decision. If it will give you peace of mind, buy a couple.