Disclaimer: I work at Backblaze. The answer to pretty much any question is "sort by price". :-) The SAS-expanders are just a tiny bit more expensive, or at least they were the last time we checked. We were worried early on that many other designs seemed to prefer the expanders vs the port multipliers, but in all the years over 450 pods we've never seen the port multipliers give us any problems. Maybe they aren't as fast as the SAS expanders? But that isn't our current bottleneck so it wouldn't help us at all.