In terms of being "safe," if you mean in terms of data collection/privacy, just because big companies have an interest in Linux, that does not mean your Linux Mint install is sending telemetry back to those big companies with your personal data.
Big companies have an interest in Linux because Linux is the backbone of server infrastructure all over the world. They contribute to the code, but the code is open source, so the community could see if they were putting some kind of telemetry into open source projects, or the community could simply fork the code if a big company tried to do some other objectionable thing.

Is there some reason why you want to hold an exact temperature for the entire steep? You are always going to get some temperature drop pouring from the kettle into your cup/teapot/etc.
I know in the gongfu method, it is standard practice to do a hot water rinse of the cups, which should warm them and reduce the temperature drop somewhat. You could do something similar by filling your brewing vessel with hot water, draining, and then filling it with the tea and new hot water, but you will not eliminate the temperature drop entirely.
I would assume most recommended times/temps from tea vendors are designed with some temperature drop in mind. I think they are more like recommendations than hard, scientific values.