I wouldn't expect some convincing result in term of "real" piano or organ sound.
Just keep in mind the Minibrute is monophonic so no chord playing would be possible.
But rather than a all-in-one workstation compromise solution, why not building yourself a small setup aarngerd around a good choice of elements including the minibrute used for its own sound and as a small masterkeyboard to trigger some sounds from other compact devices dedicated to organ or piano sound.
For cheap, compact and good sounding organ sound, you could check the Ferrofish B4000+.
Regarding the piano sound , maybe an also compact size SM Pro Audio V-machine based piano VSTi could do the trick (but you would need a PC to set it up).
And as both B4000+ and V-machine have audio inputs, you wouln't necessary need to have a small mixer and could decide to use any of these 3 elements when you need them.