That is a very good question and I hope my reply below help.....
From my view, as long as a design can make "œslow currents" in refugium section, and with good filter to avoid crab, snail, pistol shrimp, etc"¦ via return pump to main tank, then the refugium is good enough to serve its main goal. Note you do need cods, pods via refugium pouring back to main tank, so your Mandarin goby can survive there.
So what else having a refugium section pouring directly in to return behind main pump section as I did in my sump design?
Beyond above "œslow currents", "œfilter" features that a refugium must-have, this design I can turn off pouring valve, create an isolate section for water change. This way, tank owner do not have to turn off main pump when running water change, and I think it benefit a lot for new temperature control and other perspectives.
The other minor benefit is since refugium which you need light, is far away from skimmer section, skimmer will have less chance to grow algae, but of course there are other ways to avoid light hit directly to skimmer section.