Well, enums are fine, but the given implementation in PR#21 breaks old code (tradeoff for better capsulation). You would get the same result by moving my "constants" into the class-public-area. Scott Meyers has done a good job explaining all the differences between defines and const/enums in "Effective C++ third edition" - Item 2. The essence is: defines are simple string-replacments in global namespace handled by the preprocessor. The later coming compiler has no clues of these replacements. By using consts you can operate in local namespaces, have to think about the type of your constant (less errors) and in case of an error you get a reference to the name of the constant involved.
I have not searched for any ardu-libs using that style. Should that be an important point? Good Practice allows current and coming compilers to optimize code as needed, regarding size, speed, ramusage.
2:
I have tested the new code in a heating-control of an espresso-machine and in quadcopter-code. so far i noticed no differences in the behavior.

2015!! What happened to this? the library clearly needs to be refactored. @orgua there should be no difference other than probably more efficient code generation. Specially using floats instead of doubles.