It's looking like the head unit is the problem, I have tried it with three different phones and leads. All gave me over 100Mbs when connected to my laptop by USB or WiFi, but down in the low Mbs and sometimes Kbs when connected to the head unit.
USB not USN :^)
If I USB tether my phone to my laptop I get download speeds of 150 to 190Mbs, If I USB connect it to my Essgoo head unit, I can only get 1.5Mbs at most, it's usually in Kbs. If I connect the phone via WiFi the results are the same, so there must be some problem at the head...