I took the plunge and ordered myself
Vochlea Dubler 2 voice to MIDI thing.
I'm actually quite happy that I did.
I tried it with my AKG mic, plugged into my Presonus Audiobox 1818VSL, but there were extraneous noise issues and calibration was difficult. Now the dedicated USB microphone has arrived, It works remarkably well, doesn't need any calibration, and just seems to work beautifully, straight out of the box. The microphone is an extremely high quality thing, with a reassuringly solid build quality.
It's a really clever bit of tech. The software understands different scales and modes, and will also allow you sing chords, as well as single note phrases.
It also does pitch bend and recognises three vowel formant sounds, A, E, and O, which can be mapped to MIDI CCs so you can control a synth filter, for example.
You can train drum triggers too, so you can beatbox drum patterns.
It's a standalone application, but it comes with a VST that it can link to, so you can control instruments directly in your DAW from it.
All-in-all, it's pretty damn good, and a great way to get ideas into your DAW very quickly, just by humming a tune.