+1 to all of that from John. The UMIK has held up very well in comparison with Bruel and Kjaer gear here.
REW currently seems stable across a range of Macs and OSX versions. In the past there were issues, fatal ones, because Apple were not complying with Java protocols. JohnPM, REW creator, sidestepped that by building Java into the current Mac REW.
However, there are still issues with particular interfaces or their drivers. e.g. RME, Firewire.
The very useful USB Mic can circumvent many of those, with playback via the Mac Line out. No interface.
REW has an extremely comprehensive feature set, it's like a Lab.
But FuzzMeasure has it's own fortes. Multichannel recording. Good for Stereo sampling using Jecklin Disc or even Dummy Head techniques. Can even do 8 mics simultaneously if you have the gear. Ditto playback, this is surround capable. FM also has the ability to generate a sweep which we can send to a client. They record the result, send back the audio, we convolute in FM. i.e. The client needs no skill nor software nor hardware other than normal recording.
Both apps can Export and Import IR's which the other can read. I would expect the iOS apps to be similarly capable.