I bought the Funcl AI Smart Headphones 
on sale from Amazon. The AI function is provided via the Funcl app that appears to only work in Chinese, so I removed it from my phone. I can access the Google Assistant by double tapping the left headset button. Some times a single tap works too, although double tap is specifically defined for accessing the phone's assistant.
A problem that I have with these headphones is that there is no on-device volume control, it appears to expect volume control to be done via the phone. The main problem I have is that there is a beep that indicates the assistant kicking in that is too loud for me and I haven't found a way to adjust it.
I have now used these headphones for a couple of phones calls and I had a good experience. I could hear the other person on the line and they appeared to be able to hear me with no problem.
I've decided to pair these headphones to my iPad Mini 5 rather than my smartphone because I was not using them. The problem is, the Funcl headphones do not disconnect from the iPad when I put them in their case, I have to manually turn of Bluetooth on the iPad to disconnect the headphones.