+1 what Hectic said
I have one of the "shock proof" ones and its been fine on my GBBR, holds zero as nicely as my old Guarder one.
The Guarder one is the nicest Aimpoint around, IMO: has a broader range of brightness settings (5 settings but there's a bigger difference between each one: from really dim for darkness to really bright for full daylight), no visible tint, a slightly finer dot size and better flip caps.
The Huang one has nice trademarks and there's a Killflash that fits onto it which is nice. Bluer tint to the optics however, and the flip caps are total crap (mine self destructed during the first game).
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