I don't have a mandocello, but I do have an octave mandolin. Don't know that I'd consider a m'cello as an ideal entry point into the mandolin-family universe, but to each his own.
Sierra Hull just dropped this little gem a few days ago.
Back in the early 80's, (I believe!) I had a Flatiron Mandocello. Had to sell it in one of my many "How in the hell and I'm going to pay rent this month?!"
I loved that thing though. Beautiful when played along with acoustic guitar.
If you can get your hands on an Eastman, that would be great. Eastman crafts some very nice instruments. Good luck!
I am building an electric one now, actually I just started it while watching football this weekend. It is going to be an Explorer-Style like Rick Nielsen’s. It’s really hard to kind information on his Hamer model, su as scale length. I’m going with 26” to 27”, haven’t really decided yet. The was a company called Dakota that made an acoustic kit, but it has been discontinued. I may also find an acoustic 12 string and modify it into a Mandocell, I’ve read some things and this seems relatively easy to do.