I can only tell you what I know. I am a user of Cirrus Link MQTT.
I’m in the Oil & Gas industry and we developed our own “Network Edge” device but it was developed with
the purpose of making sure we could communicate with Ignition and the Cirrus Link Mqtt module using the SPARKPLUG B ( 3.1.1) protocol.
We now have several of these devices out in the oilfields in very remote locations (some even using Solar Power) and they all publish/subscribe their TAGS to our Ignition sever “Flawlessly”.
The support from Ignition - Cirrus Link has been outstanding, I could ask for none better.