There are so many different versions of bronze (maybe thousands), unless you know the exact makeup of the material for a specific job, then you just can't generalise over machineability.
I have some stock of hex ali bronze, and it machines very well indeed. But that is just one version of it, another one might be like trying to turn pure tungsten, and I have come across that sort of stuff before. But both are classed in general terms as ali bronze.
Unless you are used to turning all versions (and I am not) and as previously stated, the makeup, then most people will have machining problems of one sort or another.
Where we usually obtain our materials from (castouts, scrap yards, bar ends) you just have to try to machine it the best you can, as they will all most probably require some sort of special machining solutions.
I am just machining up some Colphos (purchased from a supplier because the drawings called for it), and it machines as easy as normal yellow brass, but with slight curls on the chips. This is the first time I have ever used it, but now, because it is only slightly more expensive than PB102, it will definitely be used again. Purely because I know I won't have any trouble machining it.
http://www.columbiametals.co.uk/products/details/?id=88&trademark=colphosSo really, in our small world of engineering, you just have to suck it, and see what happens.
John