The sound isolation is quite good and the sound quality is acceptable. However, I find that they are uncomfortable to wear for longer periods since they squeeze the joints of my jaw. I guess that depends on the size and shape of the head of the user, though, but I have not had the same problem with headphones from more expensive brands.
Another complaint is the build quality, which is quite poor. The plastic brackets that hold the earmuffs to the headband started getting loose after having used the headphones for half a year or so. I reinforced them with a piece of scotch tape, but otherwise I think they would have come apart altogether after a few more months of use. The headphones still work fine after a number of years of intermittent use.
The price is of course unbeatable...
All in all, these headphones are fine for recording purposes as a backup when your main ones are out of reach, as an extra set in a pinch when you have more people in the studio than expected, or if you only need to use them so rarely that you cannot justify spending more money. But for your main cans, I recommend choosing a more expensive brand.In any case, do not use these headphones for mixing.