I have a Mengascini. I'm not sure of it's model number - it has 7, not 5 on its helper row, and 12 basses. There are two treble side under-keyboard switches, and three bass side register switches (full, thirds out, thirds out and reduced bass). The treble side is fifth button start, which is perfect for a D/G, as it takes out the top squeakiest notes, and adds in some lovely low notes, permitting lots of flexibility below middle C.
It's a lovely instrument. A little heavy, but all instruments of its size are. Everything works beautifully. It's quite polite and refined (to my ear) in its sound, but has plenty of oomph if worked hard. I've been gigging with it for over 4 years now, and it's holding up very well.
All in all, I'm very happy to recommend!