Right. Future availability is a risk. Even todays availability is very limited, I had to order from USA. That means slow delivery and shipping cost may be high. The cost of the cassette is also fairly high (though likely less than a one-piece cassette). In addition to that is the weakness of the hub. So many reasons to avoid it, except if planned to rebuild it anyway. In that case, one could choose whichever R&M Birdy variant is cheapest - or whichever has the best cost-to-resale value of the parts to be replaced. That might be the 8-speed IHG variant, at least if one plans to go 11-speed or higher, and have to replace derailer and shifter anyway.

I agree with XDR, either that or IHG. It would be good for R&M to switch to that too. It allows both road and mtb (with adapter) cassette variants. The SRAM 10t cassettes are easily available, including some cheaper ones. And other brands provide compatible 9t variants. It's a more customer friendly solution than the Sunrace.