Here's a picture of Geib himself with a Geib Conn. I've never played one, but have played Warren Deck's souped-up model. It had a broad sound, but some devilish quirks.
That old Conn on e-#%y was listed as a Helleberg Conn, but it wasn't. Helleberg, according to reliable sources, only played rotary valved instruments, ERGO that couldn't have been an instrument built for Helleberg. There are still some questions about the name as far as I'm concerned.
...ahem
Confusingly, those particular tubas are still often referred to as Helleberg Conns and Rudy Meinl even makes a "Helleberg Conn" copy.
I have never played the Conn version but the Rudy "Helleberg Conn" was good, with some ($10,000 worth of) reservations. It's a smallish 4/4 size, not large at all. Similar to (not the "same as") the CB-50.