Well I came into an organization that used a custom soft PLC from a contractor that only supported function block that matched this spec. It was horrible but that was I think largely due to the implementation. I came in and helped select the next PLC which was between ISaGraf and Rockwell both which support this standard. I wrote a converter to port the whole thing to Rockwell function block diagrams.
Most of the control developers would only use function block and ladder at that time and would not consider structured text because that was too much like programming. However after a little introductory training on how much easier it was to do a lot of the stuff in structured text that was horrible to read/write in function block they will now only use structured text to develop.
My comments on this are function blocks are really only useful for PID loops or similar real time functions where you have a handful of inputs and outputs. I’ve seen some useful stuff in LabView, BizTalk or SqlServer Integration Services where the function block/flow diagram works but generally I have only seen it as cumbersome and gets in the way and offering little value. Not criticizing and I certainly dont have the widest exposure to other users of Ignition.