The problem with the M8 I think is the ball-joint they used at the end. take a look at the final joint on the M10 where it mates to the monitor, see how it doesn’t use a ball? It uses a double joint there instead with one for left/right rotational, and a separate joint for up/down.
This arm from Ergotron has the same articulation as the M10, advertises it can support up to 42 pounds, and it’s a lot cheaper. That’s why I suggested taking a look at the Ergotron arms. HX Desk Mount Monitor Arm | Ergotron
Honestly, I wish I had known about ergotron before dropping for the M10, likely would have bought that instead.
The M10 is more polished and fancy looking, and can support up to 48 pounds… . but the Ergotron is much less expensive and is still quite solid at a 42 pound rating.