Coincidentally I was at the bike shop today and test rode the Tern D8 you were eyeing.
It rode very relaxed and comfy with the upright posture and fat tires.
The grip shifting was very smooth and fast too.
The wacky rear derailler would concern me if I wanted to upgrade, its not a standard mount.
Tern really stiffened up the folding stem area.
I'm sure it flexed some but not in a worrisome way like the old Dahon Curve I had.
It will never feel as solid as the Smooth Hound but I would not hesitate to buy the Tern if seeking a portable and solid cruising bike.

The nice thing about the Dahon midtowns are the standard size components.
Everything except the front hub width is standard road size componentry so upgrading is only limited by your wallet.

They had none to test ride, but I lifted the Verge X20 and that thing felt pretty light, but it was $3000 in Bangkok.