With OpenWrt each single device becomes a router by default. Even if you install OpenWrt in a fridge.
But the real intent of ZyXEL with these devices are to use them as Mesh access points, so you would be buying a ton of them (hence the price). I think this is why they are not releasing sources yet (they told me in a recent email that they will release it by the end of summer, and before they told me they would release it by May, so they keep posponing this for obvious reasons)