Are nested subflows a problem?

In the real device all sorts of operations will be done on temperature and power. This is just a simple example I made to understand how this works. If all I needed to do was multiply a number by 2 there are obviously much easier ways to do that. In general I just need to get temperature and power (and a bunch of other variables) into a flow so that the device can establish setpoints and run operations based on those setpoints.

Yes, the msg = msg was ridiculous, I have removed it. Thanks!

Here is the original thread that started all this subflow discussion. It has background on what I am looking to do with this multi-channel device: Join the json code from multiple flows into one file

But in general, are nested subflows bad, good, unreliable, or perfectly fine? I found one post on stack overflow where someone else is doing it... https://stackoverflow.com/questions/49559267/organize-subflows-in-palette