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There's one here in town , about a year old and it plats just like you imagined . A Cerveny tuba that wraps around you . Perfect for those mounted on horseback gigs . The build quality is also excellent . Ed

I have owned one for a few years - plays very nice - big solid sound, in tune, good valve and linkage action (but the paddles are a bit prone to being bent sideways.) The hand position is not perfect for me - I have to rotate my wrist to the right just a bit - but it is not too uncomfortable for 3 hour gigs (with breaks.)
The mouthpiece position is good for me, with one bit. The body loop is smaller than most Sousaphones, so it might be a tight fit if you are "a Portly."

I bought mine unlacquered, but after a few weeks I had it coated at Best Music.

Lighter than some 4 valve sousaphones I can think of, at 18.5 lbs.

Rubberlips wrote:

The hand position is not perfect for me - I have to rotate my wrist to the right just a bit - but it is not too uncomfortable for 3 hour gigs (with breaks.)

Thanks David - you confirm what I suspected from the Cerveny advertisement pictures. I have also seen some historical advertisements of marching military musicians having to bend their wrists at nearly impossible angles.
What a pity.
Ordinary sousaphones have their valve assemblies lined up correctly so that the hand meets them at a natural angle.

I saw a rotary valve helicon at a San Jose Tubafest Xmas one year with the paddles in perfect position - the valve cluster was in the same alignment as most piston helicon/sousaphones. It looked very comfortable! (sorry, no pictures or other info...)