I have one HX Desk Dual:
Choose a monitor arm that’s as adaptable as you. With the HX Desk Dual Monitor Arm, you can easily reposition two 32" monitors while still enhancing your workspace with a sleek design.
www.ergotron.com
And one HX Wall:
Choose a monitor arm that’s as adaptable as you. With the HX Wall Monitor Arm, you can reposition large monitors weighing up to 42 lbs (19.1 kg) while still enhancing your workspace with a sleek design.
www.ergotron.com
I have swapped the top parts between them a few times. In both cases they have been fine, and I am actually using the dual arm with a single ASD currently by simply removing the side arms and mounting the monitor in the middle instead. This also works perfectly fine, and I am happy with it, no complaints.
(Possibly moving it requires more force than intended because the ASD is light and I have the screw a little tight. At most it is a little annoying, but definitely not a problem.)