For the price they are good. Better noise reduction rating muffs cost significantly more. Just make sure you use good quality ear plugs and fit them well with the muffs over them.
I personally prefer using passive muffs NRR30 (Peltor Ultimate 10 series) with plugs underneath indoors and only use electronic muffs with plugs underneath outdoors.
Indoors you have much higher exposure to pressure waves due to a confined space which gets through your nose/mouth/bones making it necessary to have a higher Noise Reduction Rating (NRR) than one would have outdoors to avoid potential damage to your hearing.