I can tell you: excellent, with or without 2x Apo-extender. One of the best medium telezooms ever built.
But - many of these lenses have contracted some haze over the years and will need a bit of professional window-cleaning. ROM or no ROM makes absolutely no difference. Make sure you get a proper adapter the new Leica one or Novoflex; the Leica Leicina one is problematic for fit and will vignette.
(In the end I don't use it that often for daily use. I have a perfect Olympus Zuiko OM 75-150 which is still very good optically and very much lighter and smaller thus easier to carry -and dead cheap. That lens needs distortion correction in postprocessing; no big deal.)
@ 200 mm wide open:
With 2x APO-Extender @ 200 (AKA 400 mm) wide open:
And 400 mm once again:
And finally one @ 80 mm:
BTW, the focus peaking of the 240 is optimized for long lenses and works very well and precisely on this lens and other teles. Far better than the Sony variant which is conceived for short to medium focals.