When I first got it, it was very responsive and always locked up. I'm a very patient person when it comes to bearings breaking in. I gave 4 months to break in. I was consistently throwing it for hours and doing high-stress combos. After the end of the 4 months when I first got it. It was a bit better than when I first got it, yet it was still horrible, and it was still locked up. I decided to do maintenance on the bearing; it was fine after a few throws, then it locked up. I used One Drop V4M lube and it was still locking up. I had my last option to use dark matter, so after using it it played ok for a couple of throws. Then it locked up again and had a horrible rattle sound to it. The bearing had an outer race, and manufacturing scratch marks on the outer race. It wasn't just my only one out of 100s of DIF-Yo-KonKaves. Many people are having the same problems. I'm not the only one.

Purchased the sizeD bearing as an upgrade to my Don. Quite disappointed in the end. The yoyo became more vibey with this bearing :(

Bought 2 size C konkave, both came pretty gritty with both having oxidation on the outer race and one having manufacturing scratch mark on the outer race. Used one for around 15 min and it pretty much died, making a krrrr sound when free spin with noticable vibration. Oh, and there are also a lot of horizontal movement on the outer race, definitely isn't very high-precision. Seriously, I paid $14.5 for each thinking it would at least give me a nice smooth bearing with polished outer race, I'm expecting a concave OD 10 balls here but all I got is a $2 Chinese concave-level bearing.

Got the size A bearing. It works perfectly but the surface is slightly oxidized.

I got the $30 ceramic bearing and it didn't disappoint. Very solid build quality & very smooth. It has the crispy "ceramic" sound which is super entertaining. Definitely give it a try if you want to test out the ceramic bearing.

Would I buy it again though? Probably not. I have to say the NSK KK/CT/DS bearings are still the best bearings that I've ever tried. They are even smoother & quieter than this one (plus $10 cheaper). This bearing is not bad at all, but there is a better choice with lower price.