I have had 2 clearwater scrubbers, a 200 and a 50. They work no debating it. I would venture to say better then your normal chaeto refugium. When I had the 200 on my 100 gallon it was pristine zero algae, running undetectible zeros feeding literally as much as I wanted (5 cubes a day plus nori to tangs). Which is even more impressive since i had been battling turf algae, came with my used rock, for 2 years with phosban and phosphate rx.
Now why did I get the 50? the 200 is huge and hard to work with under a stand (even a larger then normal stand). I had to downgrade to the 50 to make life livable maintenance wise in the sump. the 50 seems to handle about 2-3 cubes a day but have around 5 nitrate and ..05 to 1 phosphate.
Okay downside. They are not external they must be placed somewhere to drain back into the sump, such as over it. Because of how algae grows on the screen it can clog the slit pipe it can send water dripping out the pipe entry. This happened twice to me, once in a comical fashion where a thin stream of water was shooting out the top 3 inches away (not comical at the time lol).
If you have the space pull the trigger.