The neat thing about the electronic ones is you can hear small sounds around you yet the muff "clamps" down on all sounds over a certain db level. I agree with Jay above that they don't isolate you from other sounds. If out by myself, I usually use a non-electronic muff, depending on where I am.
Whatever you use, USE THEM! I have constant "crickets" sounding off in my ears from past sound abuse.
"We must reject the idea that every time a law's broken, society is guilty rather than the lawbreaker. It is time to restore the American precept that each individual is accountable for his actions." - Ronald Reagan