This mirror is designed to sit on the end of your handlebars and give you a view of what's behind. As well as being suited to straight bars the mirror can be used with drop handlebars or most bar-ends just so long as the internal tube diameter is 16.5 - 20 mm.
The mirror does not take from the handlebar length and you will not need to rearrange brake levers etc. to install. It is designed to be robust and folds away when not in use.