At several schools you can add a 4th letter writer, so if you think that this difficult professor's letter won't make you worse off you can always pop them on for those schools only.
Congrats on an R&R! That should speak really well for your sample.
Like Dreams said, you should probably reconsider the schools you're applying to if you don't think you'll accept an offer from them if you had no other. But I don't think you should spend a lot of time researching them if you're applying to 10+ - it's a good way to piss away a lot of time, better to look more seriously at them when you do have an offer. It's not much work for a prof to upload their letter to one more school, but it does cost you a fair chunk of change.