I know that this is an old thread, but these posts were helpful while I was researching longneck sopranos. I ended up considering the concert neck Flea ukulele, the Sailor Brand ukuleles (14 frets to the body, but apparently not a concert neck, but you can have it customized with a concert neck for extra), and a Mahalo UK-320SL (available in Japan only for some reason).
I ended up buying the Mahalo UK-320SL (via
Amazon.co.jp using a forwarding service called
Tenso since I couldn't get it shipped out of Japan otherwise). All in with shipping, it ended up costing around $90. The top is solid mahogany. And while some sites claim that the back is solid mahogany too, it's hard to confirm that via google translate (and I don't know how else to tell). The side are laminate. The nut is bone and the compensated saddle is NuBone. There are dots on the side of the fretboard too. Came with cheap friction tuners, a cheap gig bag, and a "Learn to Play Ukulele" DVD.
I know that a lot of people think Mahalo ukulele's are crap, but I really like the sound of the UK-320SL. It's loud. The sustain is good. And it's got a nice woody sound. The action was definitely on the high side (~5mm on the 12th fret), and a bit high on the nut. I've managed to lower the action a bit to around 3mm, and lowered the nut slots too. The intonation is a lot better now, but still goes a little sharp further down (which I'll try to address). It has a much better sound than the Kala GAC or SLNG that I had tried. It's also louder than the GAC despite being a soprano. I don't know what kind of (semi-white) strings it came with, but it actually sounds pretty nice.
There's a
video on youtube.
Overall, I'm really happy with it, and definitely for the price.