Electronic muffs differ from passive muffs in that they use a microphone and amplifier to bring you the sounds of the outside world. They then protect your hearing by limiting what they let through. The big difference between the cheap muffs and the good ones is the way they go about limiting harmful sounds and how well they work. The cheap muffs shut off the microphone when they detect a loud noise. What that means for you is that you get a stutter effect and when the instructor is talking during shooting he will get cut off with every shot.
Bottom line this might be acceptable for normal range trips but it sucks royally when attending a class. The real cheapies intended for use with power tools also tend to react too slowly to loud transient sounds like gunshots. In other words by the time they kill the mic some small amount of damage may have already been done.
Instead of cutting off the mic good mid-priced muffs like the
Peltor 6S and
Peltor 7S adjust the volume of the dangerously loud noises (and only the dangerously loud noises) down to a safe level. What that means to you is that the instructor comes across clearly even while there are rounds going off in the background.
Bottom line you hear everything normally but nothing is loud. The 6S doesn't really block enough sound (19dba) so of the two the 7S (26dba) is a better choice. Both are kind of big and are thus better suited to use with a pistol than a rifle or shotgun.
What the step up to premium grade headphones gives you is smaller size, quicker response, and some really nice bells and whistles. The pricey
Pro Ears Predator Gold are small and cupped to clear the stock of a rifle or shotgun yet block as much noise as the bulky Peltor 7S. They react extremely quickly adding to their protection. They also provide up to 7db of amplification for use while hunting, investigating noises at home, or listening to the instructor. Finally they shut themselves off after a few hours saving batteries should you forget.
I use the Pro Ears Predator Gold and recommend them highly.
With any of these I highly recommend bringing spare batteries to the class.