Thanks ChesterTheBunny for the link.
The way I read this is, that it is still microfibre and they have put a flannel name on it to give it a different perception. It still comes down to being polyester ... and what you like or do not like about that.
I would see no reason why not to use it for a backing, or as in their photos it appears they made the whole quilt, both front and back with it.
Have you ever used fleece for a backing? I am betting this is basically the same, just that it is thinner and promoted to not pill as cotton flannels or fleece both can do. And yet, there are some flannels and fleece that do not and stay incredibly nice throughout their lives.
Polyester does not breathe, and one of the reasons I do not care for it ... and yet, I have one quilt with a fleece backing, and if I am cold, I will grab it, as I know I will be warmed up quickly, because the heat stays with me.
It all probably all comes down to personal preferences.
What you may like ... I may not ... and vice-versa!
If you are intrigued, why not get a piece of the fabric (or buy a sheet) to use as the backing on a small quilt and see what you think of it?