I have been using Mixedinkey for a while now and I feel it's more accurate in the bpm department than the analyzers from Mixmeister Fusion or the (used to be free) Mixmeister bpm counter.
Both offerings from Mixmeister only handle mp3, I have used them as long as I can remember but have now retired them.
Mixedinkey 10 is a one-time payment (look for festive sales) and does require a constant internet connection, to verify with I guess their own database of meta data (speculation on my side)
The KEY detection is more precise than Pioneer Record box or Mixxx (which I tested for months both before going paid)
Reason for buying Mixedinkey 10 is that it's very stable, it was running for 1+ week 24/7 and didn't cash or became unstable, no bad things to report.
I like to multi task a vast list of audio tools and my Xeon kept from breaking a sweat or limping on one leg, Also Mixedinkey is gentle with system ram, it never used my 32gb, not even after a week of running on 300k+ mp3 & flac files, drag & drop works flawless.
I'm pretty new to ENERGY level detection but I guess it could be help as guide to know which song could be played next to follow the intensity of a song.
All meta data in general are only to be seen as helping out, it's not always spot on and you stil need to make your own choices

The good part is that mixedinkey writes data directly in MP3 or FLAC files, and that MusicBee can read that meta data and allows you to sort als the various columns you can make in your custom views, create auto playlist from that data etc etc.
Besides BPM, KEY, ENERGY, it also auto detects and can (if you select it) write CUE data directly into the MP3 or FLAC file.
Various DJ software can import those CUE (hot start points in time) and through a few steps, Recordbox, Serato and others will be able to make use of that.
I keep on mentioning that it uses MP3 and FLAC but that is because I only use those 2 formats and have tested both with a couple of hundred thousand files, it works well.
Tony_D.