very usefull when you want to keep an eye on your rig while away from it, you can even restart it, overclock, undervolt, check temps, and musch more while using the free edition. Honestly, i couldn't ask of anything more (except for a few things, but they are covered by the paid version)

Good control site, much easier to set up and control then hiveOS. Also has many more options. Unless you have multiple rigs, i cant actually sugest you get the paid upgrade, its not worth it. good for multiple rigs though obviously to have them all in one place.

Minerstat is really easy to use (configuring the actual miner can be complicated though). I switched from using the desktop version to the minerstat OS and it has worked flawlessly after properly configured. Any instability I had in windows is just gone as well, and getting more hashrate and efficiency out of my system now.