I've used Marsee magnetic bags on several bikes and they are a good product.  Their 'Teardrop' style works best with the sloping tank on the LS650.  The current versions have side flaps, the previous had cleaner lines without them.  I'm using the older 20 liter bag which hides half of the speedo but it holds more stuff---a full bag of groceries with the top popped up.   The 15 liter bag (also a pop-up) will show the whole speedo.  To keep the tank pristine, place a sheet of 3M static film on the tank.  This is the stuff prints shops use when making static window decals.  The magnets still cling strong but the vinyl barrier prevents chaffing from dust.  

Marsee:
http://tinyurl.com/5g3jd

My 20 liter:
http://tinyurl.com/6xmhr