Shaun, I suggest you try them. Everyone I've talked with privately and all the posts I've seen about the M5 bookshelves or in-walls, say very good things.

I decided to not do the M5 on-walls. The M5s on stands are just perfect for me. Maybe I'll do actives in the future. There are a few reasons for my decision. First, I was drawn in by the real wood (mine are vinyl oak) and was dreaming about rosewood. I've been advised by a couple of friends to not do it because they'd detract from my primitive weapons walls. I can now see their point. Second, I love how they sound and know darned well if I go on-walls, the soundstage will not be as magical. I was reminded again this morning of how much I love their sound when I was listening to Vinyl Jazz on iHeartRadio. The tunes out of them were incredibly seductive. Third, someone very high up at Axiom told me in a very polite way to stop f*c$ing with my room because it looks and sounds awesome. laugh

If you have to go with on-walls, I suspect you will really like the M5s.

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated