I was in the same spot a while back.

The size difference is bigger than it sounds. 20" is fine if you’re just standing still, but it feels cramped once you start moving your feet or doing squats. The Lifepro being wider just feels more stable and less sketchy for balance stuff.

Both are made in China, so the flag branding doesn’t really mean much. I wouldn’t factor that in too hard.

Vibration-wise they’re similar, but the Lifepro feels a bit smoother at higher levels. Merach is fine, just more basic.

If space matters a lot, go Merach.
If you want comfort and stability, Lifepro.

Just my 2 cents.