If the $30 are the ones I think they are, they range in price from $19.95 on sale to $39.95. I have two pairs for guests. They work moderately well for hearing protection. They are mono, not stereo. Sound quality if nominal to poor in terms of tones. The noise abatement is absolute and fast enough, but the return to hearing is slow. For example, my Peltors will cut out the loud sound for the duration of the loud sound, but the cheap muffs have a delay that extends for about a half to one second after the sound. So they can make conversations a little more difficult. Also, they seem overly sensitive to sound and can cut out from somebody just speaking too loudly.
Given that I wear plugs with muffs, when the sound cuts out, it is difficult to hear any conversation with both plugs and muffs in place, so the delay is bothersome. Also, I think the stereo feature is a good thing. Being able to hear a sound and know what direction it originates is a good safety feature.
For the money, they aren't bad, but they aren't what I would want all the time.