Top tube bottle mount: Dahon's have this, but a) bottle nozzles often leak when horizontal, and b) cage was frequently hit, no matter how careful I was, with foot when mounting or dismounting the bike, laterally bending the cage. Once I mounted the aero bar and bottle, I took it off. But I left the cage screws, to keep out water in the rain.

Seatpost clamp: On my folder, a previous frame cracked at the seatpost clamp slot (in front instead of back, wrong location), both due to stress from rider weight, and too much distortion there due to excessive compression of plastic bushing when clamped; Newer frame has aluminum bushing, far less compression and adds strength, but still more movement there under clamping than is desired (for ease of seatpost sliding when folding). I don't fold often, so I added, between the bushing and seat tube, a 1-thickness wrap of soda can side material as additional shim, full length of bushing, cut easily with scissors as it's soft, and now it clamps with almost no movement. More difficult to move seatpost up and down when folding, but worth it to me for perhaps better frame life. Because between factory shim and seat tube, doesn't move when sliding the seatpost, if I make sure to hold the clamping collar down when pulling the seatpost up.

Rattle: I have a Dahon, not a Helix, but I promptly removed the magnets for folding front and rear, were rattling, and unusuable once I installed rear rack (has disc spacers, which I don't need) as it prevents perfect 100% folding.

At least with your single-sided cantilever front hub, you don't need to remove the wheel to fix a flat. That appealed to me regarding the Giant Halfway circa early 2000s (front and rear), the first folder I ever saw. But glad I didn't buy it due to the drawbacks of that design in terms of mounting rear rack and such.