All guitar effects/distortion pedals/boxes will work perfectly well for an electric ukulele.
If it's a good product for electric guitar, it will be a good product for uke.
Can "distortion"- pedals not be used on instruments with passive pickups and nylon strings?
They can be used, no problems.
It does not need to be a magnetic pickup, although a magnetic pickup has more sustain.
The Risa NYLON electrics have heaps of sustain though compared to other nylon string electrics.
The A string keeps snapping. Any ideas how to avoid as it looks a bit like a design flaw.
I've had Risa ukes for years and never had a string snap on me. Perhaps email the people at Risa before jumping to such conclusions..
To be honest, this new prototype is just a cheaper and more portable steel string electric from Risa.
Steel string electric ukuleles are nothing new for Risa - their other steel string electric ukes have been out for years:
http://www.youtube.com/watch?v=rrTto-UimHg
I don't see it as a superior instrument to nylon string, but a "different" instrument - as a classical guitar differs from an electric guitar.
I really like the nylon string Risa electrics:
http://www.youtube.com/watch?v=NuqQWon71do