The M2 gives improved off-axis performance compared to the VP100. Any centre speaker is a compromise between performance and convenience. A vertical array of drivers results in a more linear response than horizontal.
In the case of the QS10, sound comes from 5 sides. They are not too big for your room. I had the QS8v2 and they were puny compared to the sound I get from the QS10. Read my review on the QS10 product page. It's the first, long one.
I tried them on the back wall in my room. Side-wall placement results in a more immersive and accurate experience. This isn't a fault with the QS10. It's how our ears-brain perceive sound from the back vs. sides. It's worth trying back vs. side to see what you think.