love a good tank bag...
opinions will vary widely...
here's mine:
The Rapid Transit Recon 19 rocks.
https://www.motorcycle-superstore.com/14/71/986/3414/ITEM/Rapid-Transit-Recon-19-Magnetic-Tank-Bag.aspx
magnetic, great scale for the FJR, big enough but not too big.
narry a scratch in many years on the bike, the trick to no scratches is i routinely carry a microfiber polishing towel (small) in the tankbag. if i see dust or grime, i wipe it down before placing the tank bag. i also am very careful about keeping the contact side of the magnets wiped off. just a quick once over of the tank and magnets ever now and then, and you are good to go
another tip is put on/take off should be done with care. I personally mount the bag, nose first, while holding the side magnets up then gently put them in place then drop the tail magnet into place. easy. i remove in nearly reverse fashion, by pulling the tail straight up, then one side mag then the nose and lifting straight away from the remaining side. the point being, the magnets never slide or twist on the tank. straight on/straight off. sounds complex, but it's easy.
this bag is roomy and holds stuff in a nicely organized way with lots of side pockets inside and out, as well as change holder/key holder/earplug pockets, sunglasses cubby (which also holds GPS or other goodies in the nose. also has an attached rainfly that is easily deployed out of the nose while riding and pulled over the bag. you want it attached, as i've seen several friends lose their rainflys as they were not secured properly or attached.
the only one downside is that the Iphone in any type of case (i use the magpul iphone cover) is a tad tight in the phone compartment... it does have clear vinyl and can be used without removing the the vinyl...
a new, and perhaps better suited bag for iphones is this. i will be looking into it when mine wears out, which seems to be a long way down the road, as it's going on close to 8 years on the road
this is the one i will consider for replacement
https://www.motorcycle-superstore.com/14/71/986/28884/ITEM/MotoCentric-Mototrek-19-Tank-Bag.aspx?WT.ac=SLIsearch
good luck in your search, and once you go bag, you never go back
i'm sure there are better bags... but for the money, the rapid is a great bag