They're cheap because they are crap. Bought one a couple of months ago, first time out when I tried to zero it the whole left-right adjuster totally unscrewed from the body as the cap was stuck to the adjuster. Eventually managed to separate them, the threads were dog rough and had galled. Replaced the adjuster back into the main body using threadlock to fix it solid. Tried to zero it but it was useless and wouldn't hold it for more than a few shots even with the parallax adjusted down to 25/30 yards which is dead easy to do. Tried it again a few days later with the same result and it went in the bin.