Yes, the Gator Frameworks Heavy Duty Keyboard Table will offer much better stability due to having 4 vertical legs.

The K&M Omega Pro has a slight front to back sway because it has only 2 vertical legs.

As you add more weight with the 2nd and 3rd tier, you should expect to notice more of this front to back sway.

The Gator Frameworks Table Top Style stand will be the ideal economical choice if you plan on supporting a single digital piano.

I do not see a way to add a second tier.