Great product, but maybe some info can be provided on the site regarding use (if applied wrong, is difficult to remove whilst keeping the painting underneath unaffected.)
Things to note would be: hold at least 30 cm from painting and move the can quite fast but consistently across the canvas while spraying. This will only apply a very thin layer, but this is the best way to go about it to avoid it dripping down your work (ideally, your painting is only catching the mist of the spray instead of the spray itself.) You can add subsequent layers applied in this fashion to thicken up the varnish film to what you want.