I used it to compress a Lazarus (open source Delphi clone) executable. The results were great (executable size reduced by more than 50%, iirc from 2 mb to around 800 kB).
Offering a sub MB executable in the era of 100 MB electron apps is totally pioneer :)
I've seen some posts about it over here recently and believe the critical users/developers mass to make it a successful dev system is achieved, however it still has to struggle to be taken into consideration in some contexts for not using a major language. If it allowed to build GUIs for C++ (QT/*TK and other builders are not even close to its usability level) it would probably become mainstream in a week.
Sometimes i wonder how hard it would be to make some C++ Builder-like modifications to Clang (like Embarcadero did for newer C++ Builder versions) to allow it use Free Pascal objects directly for people who really want to avoid Pascal.
Of course to do it properly it'd need:
* A modified Clang (or other C++ compiler) that can use .ppu files with the necessary C++ language extensions for properties, callbacks, sets, enhanced RTTI, etc
* A C/C++ library that uses the Free Pascal RTL for all memory operations
* Lazarus' CodeTools to add C++ support for automatically creating missing event handler code (and removing unnecessary code), handling syntax completion, code completion for missing identifiers, property getters/setters and private fields, inherited fields, etc to the same standard as the Free Pascal code
* All the involved teams to agree to play nice with each other :-P
Also if such a thing would be done, judging from what most Lazarus and FPC devs do so far, it'd probably be done in a way that is as compatible with C++ Builder as possible.
TBH i don't really hold my breath, but who knows, weird stuff has happened before in both FPC and Lazarus :-P
Offering a sub MB executable in the era of 100 MB electron apps is totally pioneer :)