I use it a lot for making mic mixes of different IRs into one single IR. The only gripe I have is that it doesn't allow you to export .wav IRs even when the IRs you load into it might be .wav format. I understand the need to preserve the .syx IRs that are proprietary to FAS, but IMO, if one is loading up only .wav IRs , then CabLab should allow exporting .wav files as well.
AFA Dynacabs in CabLab4 is concerned; it is a pretty great tool, too. I have three cab packs (YA Mesa OS, Friedman Redback, and 1960TV) and between these, I don't think I will ever exhaust the full potential of these in my lifetime. It also feels cool to virtually own these cabs in a way—you have all the tones you can get out of the real life equivalent without it taking up any floor space or making a lot of noise. I also have the ML Sound Labs MIKKO2 and MIKKO REFLEX plugins which do a similar job so it might be worth exploring that if you are looking to dive into this format of IRs. I got some of the best Vox IRs from MIKKO2 which is otherwise VERY heavy on 4x12s.