In-mast furlers are a better setup than the external 'add-on' style shown. Luff sag, and the 'slot' between the sail and the mast minimize the effectiveness and the lack of roach on the sail makes things worse.
In mast furlers do away with the slot/gap but do share some of these other downsides. However unless racing many will embrace the convenience, and sadly furling mains are becoming almost standard on many new boats today. And if not racing, the performance hit is probably not a big issue for most.
Like many things sailing, there are fans, detractors, and converts. Furling mains are not for me....... yet..
This has been discussed before at length.. do a search on the topic and you'll get pages of reading to do...