Well, as to the numbers involved, in the USA (as I think it said in the previously posted news feed) about 200,000. Total here in Oz, I could not say but we as a company have some 2700 active units under our "care".
Problems?
Batteries
Screens
Air in line sensors
the "will not turn on at all if the tube release is not set correctly" problem
and others that have been discussed elsewhere on this forum I do believe, if one were to use the very useful search function so thoughtfully provided by Huw , eh Geoff !!

and that's just the general/everyday technical never mind the clinical which I am not qualified to comment on. Perhaps others would care to expand on that.