the smoothest experience of ~20 tested similar add-ons
+ bold and clear 2-clicks interface, doesn't steal precious space on the toolbar (adding button on the page instead)
+ offers only few most appropriate formats
+ saves proper names
free version is limited to 720p mp4 (fair enough), reasonable donation unlocks hi-res and mp3 features.
worth to tell these limits clearly in the description though - to filter out hunters-for-free-beer.
recommended without doubts.