I have dealt with phpBB in many cases, have installed it on many clients and customers forums, and even used it for a personal forum of my own back in the earlier versions (when 1.x.x. was out), though I would not attempt to place it back into a production run.
I am speaking from the current version of my review and personally, editing HTML templates all over the place is not my idea of how customization should be done. Saving HTML files and images takes more time and space than saving a single style file and the images.
I have not used or installed the new version(s), but if it or they are like the current using HTML templates and not using an actual backend for the template system, I personally would not install it.
Uploading files over saving to a DB takes longer, it may not be a great deal longer, but it does mean it prolongs my work because I have to work with more things open then I should have to

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I cannot bash phpBB, the creators and such have came a long way from nothing, they have made a name and it does stick, but I would not use such unless they change a few things around.