georgelesley,
To date, I have only used the Straight Talk device in Oregon, Washington, California, Idaho, Nevada, and Utah. And, so far, other than in areas of marginal cell coverage (voice), I haven't had any issues with the device or it's coverage. So I have no idea how it would work in the mid-west or east coast states. Again though, it is likely slower than other solutions you may be considering.
I am a minimal user and since I never (yet) am out for more than about three weeks at a time, the 1 Giga byte card lasts the whole trip with extra to spare. Of course, I can always purchase more data if needed.
Good luck finding a plan that works for you and please let us know what you come up with,
Steve