Regarding Untangle, I presume double-checked to make sure the Android clients were connected to the z4w's wifi, as opposed to other wifi or mobile broadband? I do see that others have reported similar phenomena on the Untangle forums... strange.
Regarding your best result, the AX6000 appears to be using TrendMicro for their filtering definitions, similar to Asus. Perhaps they're also adding some type of proprietary intelligence and/or filtering methods as well?
I would almost suggest you try Fortinet, either a FortiGate plus separate wifi (your AC3100 in AP mode, even a FortiAP) or a FortiWifi all-in-one. Hardware won't be cheap and yearly licensing is also high, but if they can effectively filter where/how others cannot, then that may be your answer. The E series FotiWifi's are N-only and F series haven't come out yet, but you could also go with a FortiGate paired with a FortiAP, which integrates very nicely. A spendy proposition, though; probably too overkill for home.
Regarding your best result, the AX6000 appears to be using TrendMicro for their filtering definitions, similar to Asus. Perhaps they're also adding some type of proprietary intelligence and/or filtering methods as well?
I would almost suggest you try Fortinet, either a FortiGate plus separate wifi (your AC3100 in AP mode, even a FortiAP) or a FortiWifi all-in-one. Hardware won't be cheap and yearly licensing is also high, but if they can effectively filter where/how others cannot, then that may be your answer. The E series FotiWifi's are N-only and F series haven't come out yet, but you could also go with a FortiGate paired with a FortiAP, which integrates very nicely. A spendy proposition, though; probably too overkill for home.