I like this... how does it attach ? magnets ?
Nope, there are strategically placed strips of velcro, with sticky tape on the tank side. As I recall, these are: around the gas cap; along the long straight-away on the upper tank; and on the underside of the tank, where the large back part (nearest the rider) folds down under as it wraps around the tank. There are also two leather strands, like extremely thick square leather shoelaces, that wrap around the neck of the bike, and just get tied together; I believe this is for fail-safe purposes.
I haven't removed the bib since I put it on before the 2015 season. I use a micro-fiber rag and different spray-on cleaners and waxes, and I can get that in, an inch or so, underneath those large flaps, where there is enough room toward the front part of them, i.e., about mid-tank.
This is very thick leather, BTW, and a couple of times a year I'll put leather cleaner/conditioner on it.
I'm aware that there are all sorts of opinions regarding trapping dirt in bibs, and possibly grinding that in, underneath them. If that's the case, I suppose a lot of folks would say to remove any bib periodically and then thoroughly clean and wax the entire tank. I'm not of that school, rightly or wrongly. What I do know is that on my Valkyrie, my knees pressing against the tank eventually did not do the paint on the tank any favors, and this eliminates that problem. I also think the bib looks nice.