My recommendation is not to skimp too much on a good tank bag. A good bag is invaluable! I use mine every ride and have been using the same one for 10-years now. Here is the brand I use and will always be loyal:
My personal preference is a magnetic bag with expandability several separate compartments internally and externally with a nice loop/handle. I've never had an issue with my magnetic tank bag and the loop makes it great for taking with you when you leave the bike. I've used mind on the H-D, I had it on the KLR with no issues. A clear waterproof top pocket is a must.
It's better to have loved and lost than live with the psycho for life!
I have this one and it has probably been the best tank bag I've owned. More than enough space to hold stuff as it is expandable, doesn't move in <<cough>> slightly elevated speeds, got your map pocket as requested lotsa little pockets for farkles and turns into a back pack to boot.