This forum is for people who are using the Samsung SmartThings ™ Home Automation System, so all of the questions and answers are assumed to be in that context.
It is a very popular forum so it often comes up near the top in general home automation Google searches, but it is not a general forum.
There isn’t any integration between Switchmate and smartthings, so I don’t think you’ll get very many responses on that.
3rd Reality are Zigbee Devices and do work with the Samsung SmartThings platform and are quite popular. I myself have three of them and like them.
Because they are zigbee, they have to have a zigbee hub. For example, That could be a SmartThings hub, one of the echo Devices with a zigbee Hub inside, or their own hub.
To make it work with Google assistant you would need either a smartthings hub or third reality’s own hub, which comes in their starter kit. (Google does not at present offer a smart speaker model with a zigbee hub built-in.)
In either case, you don’t plug the hub into a Google device. The integration is “cloud to cloud“ via the Internet. So all google devices require an active Internet connection To communicate with the third reality device, but they would for voice control anyway.
With an Echo device that has a zigbee hub inside you do have the option for a connection which is still wireless but does not require an active Internet connection. In fact, my main reason for using the third reality Devices is so that I have voice control of a couple of switches even if the Internet is out. (I am quadriparetic, so this is a big issue for me.)
It’s possible that there might be some lag due to the need to go out to the Internet and back in a Google set up, you might just have to try it and see if it’s acceptable at your house.
If you have further questions that don’t involve the Samsung platform, you might try the Reddit home automation subforum. They cover all brands.