For me, it was all about how it performs versus my KLAudio machine. This is a hard comparison to do, so all I could do was take two of my own records (which Ive never cleaned and were acquired for no other reason than testing the effectiveness of these machines).
Test One - listen, then clean in HumminGuru first, listen then clean in KLAudio. With this test, the record was quieter first time with another similar sized drop in noise floor after the KLAudio clean.
Test Two - listen, then clean in KLAudio first, listen then clean in HumminGuru. With this test, the record was significantly quieter more so with the KLAudio, with perhaps a very subtle (if any) improvement after its time in the HumminGuru.
So, not as extensive yet a testing regime as I wouldve liked, but my findings are so far:-
The KLAudio is the better machine, BUT, you cant buy them anymore and they were 7-8 times the cost of the HumminGuru, so probably unfair comparison.
The HG is very quiet in comparison, in both cleaning and surprising drying. And the drying was perfect, so big thumbs up. This could almost be used while listening to music - the KLAudio, not so much (its loud!)
For the asking price, I would definitely recommend the HG over any of the RCM cleaners at a similar price point (Okki Nokki, Project etc), however, as someone who also uses a RCM, I find you do get the best of both worlds (Ultrasonic machines wont clean oil and grease off the surface of a record).