I am personally loving the labyrinth generations. I have had up to three large complexes, (large for my standards in Rimworld anyway... meaning the size of which would take me a few months with my three colonists to build... with several nice statues, and a joy object table in each.) In one of the smaller ruins I found two, (count them people TWO), hospital beds! They are minifiable now so I could grab them up and start using them pretty darn early in the game. That was a bountiful find!
Yes, in two of them there were mechs. The one that was buried in the mountain had quite a decent number of them but by the time I excavated it we were ready to take them on.
The number of labyrinths are randomly generated - from the xml it looks like we can get as many as 6 ruins, (variations on layouts, size and potential content.) I am not sure about the mechs though? They could be added by the Core as the Core tends to add ruins with mechs and cryo caskets during map generation. Still... Curious to know!