I made tonn of devices with integrated ESP8266 module and I can say
- most of the ones with external antenna don't have connectivity issues
- ~10% of "closed" modules have some type of hardware issues, in some of the cases it can be solved by baking the module, but mostly they are throwables
- firmware is unsecure, as already mentioned
- biggest issue is dev tools / SDK, if you build in your own app into the module it can come into many "undesired" states due to bugs in firmware and sdk. Happened more than once that valid app just never get control back from the wifi blob due to bug there
None of these issues I have seen, should affect duet2wifi, except maybe the antenna part, but I went myself with ethernet version 'cause I'd never run a "serious machine" with esp8266. I, for example, have 2 teartime printers with esp8266 and they don't work most of the time. IMHO ESP8266 is ok for sensors and stuff that you don't care too much if stop working, but not as main connectivity option for a device you want to use. ESP32 so far looks much better but my experience is limited (made under 20 devices so far and while they never had any issues it's still early to say).
@Dz what I dont get is after "has 20+ years in enterprise systems and datacenters" you went with wifi option for printer??? irrelevant what module was used