I do not run skimmers and the upflow version did not work well for me. I consider it an alternate method that should be considered if you do not have the ability to run a waterfall scrubber. IMO
it is still experimental. Some have made it work just fine, others not so much. I think it works well for smaller tanks, but for anything close to 100g or more, I just think the turnover rate affects efficiency somehow, and to get past that, the build gets more complicated and you might as well build a waterfall because the cost/complexity/benefit starts to equalize.