I'm a former broadcast tv service manager.
I bought two EH50s and by the time each had completed around 220 high speed copies from HDD (months after they were one year old) both were thoroughly clapped out and I had in addition around 50 ruined DVD blanks. Additionally the displays had become so dim that they could only be seen in a darkened room.
From what I can make out, high speed dub seems to be - from the sounds it makes - very strenuous for the DVD recorder (4 hrs transferred in 12 minutes requires an extremely high data transfer rate I assume). Certainly both DVD units have clapped out in very little use. I have completely given up on them as products - I think Panasonic simply had not sorted it as a product.
The reason for the large number of ruined DVD blanks is mainly due to data corruption on the HDD - if there is data corruption on the HDD then the entire title will not be recorded (but the space will be used up on the DVD blank). However there are two ways round it One is to record at normal speed OR to find the corrupted section on the HDD and edit it out. The other reason for the ruined discs is due to increasing failures during Finalise mode where the unit would not complete and would stay forever. No button presses would exit from this mode.
Data corruption on the HDD is I believe self-repaired in the unit when it is switched off - it appears to make a table of corrupted sections and block them from further use when in the long power down mode
I now have a EX77 but quickly realised that every channel from the internal DVT receiver detected the signal as being 16:9 and thus - for no apparent good reason - not allowed to do hi speed copying. The only way around this I could find was to use an external DVT or satellite receiver and this has provided excellent hi speed copies with no problem.
There seems no good technical reason to block hi speed copy of 16:9 material - is it simply to deter people from using this facility and thus reducing warranty claims? The only reason I chanced buying Panasonic a third time was that I had become familiar with the operation and didnt want to learn again.
I suspect that the EX 77 will be more reliable but I've paid for a 3 year warranty just in case.