Garbage. Noise cancelling is minimal and mine would not charge after a single use. I tried all types of ways to recharge and they were bricked. Seen many reviews indicating same thing. I would have had an equivalent experience if I just lit 2 $20 bills with a lighter and watched them burn away. Monoprice brand is sullied by this crap. Was going to buy Monolith subwoofer - but not now...
The BT300ANC headphones seem to be very good quality; have used them a couple of times and I am pleased with their performance. I am not a heavy user and will have them handy for trips and airline use.
Positive: These headphones sound good enough for the price. The ANC seems to work as well, again I am not saying $200-$300 headphone quality, but well enough.
Negative: As a lot of 1 star reviews indicated, these headphones seem to have a problem with holding a charge. It seems this occurs if ANC is left on and drains the battery. I've replaced mine twice and have had the same issue, hopefully it won't happen on the third.
On a positive note: Outside the product issues, Monoprice has been very helpful in getting a return merchandise authorization pushed through and has been very easy to work with.