I don't know how well Leon works but Mycroft is not running locally on your own server. It's still a cloud service. I believe it can be run locally but it's very complex and not well supported. At least this was the state last time I looked at it.
For this reason (and their failed Kickstarter) I've never really been into Mycroft. After all it's kinda the same as Alexa/Siri just a slightly more trustworthy party when they say they're not using your data.
I'm just not interested in alternatives until they can run fully locally (not necessarily on device, on a local server or docker is fine)
If this Leon does what it says on the tin it might be just the thing for me.
I thought the detection engine was too complex and not fully open? I remember them looking at Mozilla DeepSpeech or something but that being one of those never ending projects.
I was asking about self hosting on their forum and they were like "just use our hosted service, you can trust us". That's not different enough from Apple/Amazon/Google/Microsoft so I dropped it.
But like I said this was a few years ago. Never looked again since.