I have an ETS800 running on my 120 now and additionally I have had the converted TF skimmer. I am also setting up a new Reef room in my basement which has a 70G sump and 30 G refugium.
And soon a new 210.The sump is filled with LR and running . That setup is running an MRC-3 beckett stlye skimmer. I like the skimmate of the TF the best but it only worked good for the first two weeks after cleaning and changing airstones. The ETS sucks ,it never works the same way twice after each cleaning but it is 8 YO. The new MR-3 works great. It maintains it production with weekly cleanings. All in all I've seen beautiful, I mean stunning SPS tanks ,kept with CC skimmers. Maintainence is key.
HTH
Tom