I've stoked and piloted the Morpheus in the recumbent shop* in Edinburgh over half a dozen miles or so; not long enough for any Audaxy comfort/speed comment, but I think it's intended as an urban utility device anyway.
I've stoked on a Hase Pino and piloted an empty one, and I would say the Morpheus is the easier to handle unladen of the two, but the Pino is the one that doesn't grumble when you throw lots of watts into it as stoker.
For carting two people around I think it's initially easier to pilot when the stoker is recumbent, compared to the Helios; the problem of the stoker trying to use their mass to steer is minimised. Long term, I'd imagine pilot and stoker will get into synch so fast that isn't a issue, so the Helios wins as a tandem, unless your intended stoker has specific needs that make upright posture a no-no..
If we're talking cargo bike, the inverted pendulum voodoo is strong with the Morpheus. I've used a Bullit for a day and found it a pig to handle in motion when fully laden, but comparatively benign at a stop since the platform is shin-height. With the Morpheus, it's the opposite. It takes a bit of foresight or brute force to keep the load stable when starting off, but once you're going above sevenish mph, it/he/her damps the wobbles right down because they've got such a long moment.