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I actually searched for one that looked most likely not to be a chinese knock off but nevertheless I saw a customs sticker on my box when it came in. It appears to work great and is of high quality optics, however I am against chinese knockoffs after reading the book "The Coming Chinese Wars."
Hasn't needed calibration in the 7 months I've been using it. As long as you don't go for a super cheap one, I don't think there's much difference. Just make sure whatever one you get has auto temperature compensation on it... or maybe they all have it and it's just a marketing gimmick!