Magnification size aside, as I see it, there are only a few reasons to choose a fixed power scope over a variable: there are less parts and adjustments to go wrong ("in a fixed magnification scope the erector lenses are held inside a stationary tube. In variable scopes this tube slides back and forth, cammed by the turning of a ring on the outside of the scope"); they are generally lighter, less bulky and cheaper than their equivalent variable counterparts and fixed scopes tend to be a little brighter at their magnification level when compared to an equivalent variable scope. Only a few reasons to opt for a fixed power scope over a variable to be sure (and there are a few disadvantages), but they are very good reasons to consider buying a fixed scope (if the power size fits your requirements) over a variable model.