I also have the mini, and have tried the midi.
I use the mini on all festools I have, and there's no problem. Now you can also have a hepa filter for the mini. I also use it for wet vacuming, and it works nice, but cannot be used as a combined carpetcleaner, though. I use it anyway for that too.
What I really like is the quietness of the mini, and it's compactness which means that I can easily carry it up and down stairs to, say 5'th floor. Others may say they think the bags fill too quickly, but to me it's not an issue at all as I don't use the TS55 and the OF1010 very much, but more the PS300 and the sanders.
I have a normal small compact Golf, and I can just pop it into the luggagecompartment, even though there's a big fat alu-bar across the space. No problem, and together with a load of systainers, I can very easily go and do my work anyplace.
I also feel it's worth mentioning, that I use a 7 meter extension cord (green) together with an extra green hose, so I can reach 7 meters, or stay up a ladder and still have the mini in another room for example. Really great for comfort of noise and that I don't step down onto the mini [wink]
The compactness and quietness is the thing with the mini (plus a hepa).
Cheers,
Jacques.