It's hard to give recommendations when you don't lnow the person, but I'll give my perspective.
The Microbrute is a great tool to learn the basics of synthesis in general and analog synthesis in particular. It is a limited instrument in terms of features compared to a lot of equipment available today, but this also means that it is fairly easy to learn.
I haven't really experienced any quality problems, apart from the sound of the oscillator leaking through at a low level when I'm not playing anything during part of the volume control's travel. Others have different experiences.
You can only play one note at a time on the Microbrute, so it can't be used for playing chords. On the other hand, it's perfect for playing expressive melodies, basslines, lead parts, and solos.
It's an analog synth of the old school, similar to synths from the 70s and early 80s. The closest equivalents are probably the Arp Axxe and the Roland SH-101. This also means that there are no memories; the sound it generates is always directly controlled by the positions of the knobs and sliders on the front panel (there is actually a microprocessor controlling some aspects of how it works, mainly how it reacts when you play notes tied together, the range of the pitch bend wheel, and similar things. You change these setting by connecting it to a computer and running the Microbute Control program).
If your son will create electronic music using the Microbrute as his only electronic instrument, he will have to record each part of a song separately, changing the settings on the synth for each part to get the desired sound. On the other hand, if he'll use it as a complement to other instruments, this won't be much of a problem. It also works well in a band setting, as long as he doesn't need to make drastic changes to the sound in the middle of a song or between songs if there is only a short pause between songs when playing in front of an audience. I use it with my band as a complement to my main instrument ( an electronic stage piano tha I use for pianos and hammond organ), mostly playing solos. I set it up for a basic solo sound and only make very small changes between songs.
Since the Microbrute is analog, it is not very good a emulating acoustic or other traditional instruments. It is, however, very good at making "classic" analog synth sounds typical of a lot of 70s pop, rock, funk, jazz, and disco music, as well as electronic acts of the day, such as Kraftwerk. It also excels at the modern, aggressive synth sounds you'll hear on today's electronic dance music tracks.
For my money, it's been one of the best purchases I've made. Sometimes, I sit with my headphones on, playing the keyboard and twisting the knobs for hours, getting lost in the sonic possibilities of the MB, but this could be because I love the kinds of sounds you can get out of it.
