In March this year I bought both the GT adaptor ring and the 4-litre Givi ST602 Tank Bag from the store here:
https://gtmotocycles.com/products/givi-4-liter-st602-tankbag-tanklock.
My review of it there says:
"This "4 litre" Tank Bag is about the size of an American football. Its internal dimensions are large enough to hold all you need without blocking the rider's view of GPS and the other important instruments. It has five different places to separate and store necessary gadgets like garage door opener and cell phone (at 5 7/8" x 3" my LG K20 cell fits but just barely). A handy "rain-proof" port on the front allows a small USB cable to pass through for the cell phone. The material is soft but pliable, will hold its shape and looks to be durable. Only time will tell if the black color will fade in the sun. Zippers are sturdy, easy-running, and have glove-friendly pulls. This Tank Bag easily "clicks" on to the Locking Ring and needs no straps or magnets to get in the way, mess with your electronics, or scratch the paint. The latch on the bottom quickly and easily releases the entire Tank Bag for unobstructed re-fueling."
I have been 100% happy with how it looks and performs. The size is perfect. Minimal view restriction and no interference with the bars at full lock in either direction (but it's close). A larger bag would definitely get in the way.
'Geezer