Fixed-weight barbells are pretty much history these days and for good reason.
Yes, they were effective for building strength, as any weight used correctly would be, but how many could you realistically buy for your gym?
Look at dumbbells and kettlebells, which are also very effective training tools, but once again you will need quite a few of them to run a good training program.
Clubs and maces are no different, in that regard. Fixed-weight implements automatically require you to buy  plenty of them if you are going to run group classes.
People who train alone can get by with one or two pieces of fixed-weight equipment, especially when starting out. Coaches, however, cannot effectively train their athletes that way.
In this video, John is working with a 45lb Adex club. Plate loading made it simple to add the weight he needed. That is something to consider if you are going to train other people.