About 10 are perfectly balanced, 10 were marginal, 10 quite out of balance. The out of balance ones cause a lot of vibration at high speed.
Parcel arrived to Slovakia in 40 days, items were well packed. The chucks fit my Dremel 3000 but there is an excessive thread clearance so you have to unclamp and tighten them several times to get acceptable axial alignment. It is obvious you can not expect genuine Dremel 4486 keyless chuck for that money.