I have had a mandolin banjo for years - rarely touching it up until the past few months. It has led me towards wanting a straight mandolin. It is an anonymous "zither banjo" which really rings out - much louder than a mainstream mando and slightly less sustain. The top two strings sound like a mandolin, the bottom two strings kick in like a banjo so it's a limited sound.
Apparently, the mandolin banjo is different from a Banjolin. The mando-banjo has the 8 strings, whereas the banjolin has only 4 strings, but tuned GDAE too. The Banjolin is often prefered to the mando-banjo as its less likely to go out of tune ( skin, humidity and heat make a big difference). There are also banjoleles which seem to be banjolin's tuned as per ukes.
There are a couple of excellent YouTube videos of a banjolin playing rag-time backed by guitar.
"What's so funny 'bout peace, love and understandin' ." Elvis Costello