I have Giant Loop, Wolfman, and . . . KLR factory accessory tank bags on separate cycles.
A lot depends upon your intended usage; going around the corner to pick up a dozen eggs; going on an extended camping ride; or charging through the boonies on as much single track as you can find . . . or, all the above. Do you want/need 99 external pockets? Transparent map window? Demounting capability with shoulder straps for backpack duty? An so on.
Just a caveat; claims of "waterproof" should be taken with a grain of salt, even from high-end luggage vendors, in my experience.
My advice: Consider the KLR bag for your KLR; easy access to your fuel tank, and expandable.
Given your criteria, I'd suggest you hie thee to a Cycle Gear shop/website, and buy one from your cost/quality decision tree threshold.
Truly useful: KLR HANDLEBAR BAG! Go on; splurge!
“You better put down that gun. You got two ways to go, put it down or use it. Even if you tie me, you’re gonna be dead.” "John Russell" (Paul Newman), Hombre