I have a Mini and 2 flex's and I love them....
Range.
Not tried them at a great distance! but have worked faultlessly for me.
I have however.... decided to use TTL cords to mount the flash to my light stands. A horizontal 580 on a flex just doesn't look beefy enough to me ( mechanically ) so have taken this step as a 'just in case' ! Gives the added advantage that the flex is 6-12 inches away from the flash and again helps any hint of Rf interference from the 580's.
( As stated, I have had no issues when connected directly. )
TTL works 'suprisingly' well. Still not made up my own mind when I am comfortable with TTL and when I use manual settings but know they will cope with both.
Load a ST-E2 to the top of the mini, use 2 flashes on the flex's, dial in TTL and a ratio on the ST-E2, use your exp comp for background ambient levels to taste... -1 stop, -2 stops etc. Click done!
Seriously, it can be that easy in the right situation.
( Normal care with TTL is still required and yes, I would use manual exposure if I have plenty of time )
HSS - again works well once you realise the reduced effective guide number of your flashes and do not try to position your flashes too far from your subject. ( It may be, was it 1 stop ?? better than the same Canon HSS set up but remember power output is still greatly reduced. )
Use of a 580 with any light modifier means it has to be very 'close' !
New beta firmware has been released and I am using it but have had no time to test any of the new functionality.
If anyone here has, I would be interested to here your experiences.
Hope this helps!?
M.