Is a vacuum cleaner a Hoover? Is cellophane adhesive tape Sellotape? Is a roof window a Velux?
Velux are the leading manufacturer of roof windows, so much so that they have entered common parlance in the trade. This is due to their dominance in the UK market place, however there are other choices.
Fakro are very well known on the continent, but are rarely seen in the UK (although they are available through a number of larger Builders Merchants). However they are generally one step ahead of Velux. Their products are different in a number of ways and it is important to be up to speed with your options in order to get the best solution for your particular situation.
Velux are all FSC wood sourced, whereas Fakro are not (most of their products are FSC / PEFC, but a couple of ranges are currently not).
Fakro have a quadruple glazed option that are amazing insulating, whereas Velux have just brought out a triple glazed version.
Fakro handles are set at the bottom of the window whereas Velux are at the top. So for many circumstances where access might be an issue Fakro can be the better option.
So just be aware that there are other manufacturers that might have the product that you want. Also be aware that you might need to look at the fitting instructions to get the right collars to ensure that you get the efficiencies required.