I thought I was not going to need it because I bought Libra from STLTones right before I knew of IRmageddon. Similar concept but still very different.
The ultimate feature is the automatic phase alignment for each of the 4 slots and the report of it to the host! I'm not aware of any other IR loading plugin doing that. But that makes mixing IRs work like a charme and makes guitar clips stay in correct timing. Another thing to mention are the various options to transform the sound on time or spectral base, may it be individual or on the master, and their visual feedback. Libra has 8 slots to work with but I think the "consolidate" feature in IRmageddon (which renders the mixed IRs into a new slot) is a good replacement for the 4 "missing" ones.
As I became aware of IRmageddon the free early access phase has begun. Right from the start the developer made clear it's a community project. We got asked for opinions, had polls about features and even a to-do list on Trello as I later saw. The handling and export of stereo files were such features or the dry/wet mix I think. Since then it continously got improved and bugs got fixed pretty fast, making it not just another IR loader.
Why I only gave 4 stars: the CPU consumption can be improved some more I think and with some settings the UI feels sluggish. Other than that I think only the filebrowser could need some more love because I think in any IR plugin the library and handling of it is the most important part.
Tested on MacOS with version 1.00.001 in Ableton & Logic. Thumbs up.