I agree with the assessment on that forum. Since the general consensus seems to be that NiMH is considered 'flat' at 0.9v, I don't see any reason that using the same rule of thumb on NiZN would overly harm them. Having said that, this datasheet (https://www1.elfa.se/data1/wwwroot/assets/datasheets/NiZn-1322-0005_eng_tds.pdf
) for AA sized cells from ANSMANN support the idea that NiZN is considered flat at 1.1v, as was indicated in the powergenix sub c datasheet you mentioned before. But, unlike that powergenix datasheet, this datasheet does indicate that the end voltage should change with the discharge current. Anyway, while 0.9v won't be ideal, it shouldn't take the batteries into that 'damaging' range (0.4-0.5v)
I've been trying to find the old powergenix datasheets, as they used to have PDF version of the manual for their 4xAA white charger, and also a datasheet for the AA cells, as well as a decent support page, but they seem to have deleted them, probably as a result of them no longer supporting them. I'm sure that charger (F100011-14 is the model number for mine) kills the batteries itself without any assistance from me or the devices used in - the batteries are quite hot the touch at the end of charge.
I have about around a dozen or more cells that when you pull them out to use after six or so months - are all at the 0.4-0.7v mark without being used - after being fully charged before being put away. For about a month earlier in the year, I checked two batches of four batteries that had had little or no use since purchasing every day or so, and charted their self-discharge rates, and out of that set, 3 were fine, 3 had dropped to 1.2 volts within a week but were stable after that, and 2 dropped to unusable within 2-3 weeks.
The reference to CC/CV charging for NiMH / nicd I made before may not have been quite correct for general purpose chargers. I was going off programmable hobby chargers that I use, which show the current and voltage parameters whilst charging, and they tend to drop the current once the battery gets to around 1.5v, in order keep current flowing without overcharging the batteries, still allow the -delta-V detection to work. The Opus BT-C3100 v2.1 lithium/nimh charger certainly does this - once the battery voltage gets to 1.48 volts, it backs the current off until the -delta-V detection triggers.
I just came across this page which compares some of the different battery chemistries (nimh, nizn, lithium) - you might find the comments on NiZn (starts about 1/4 down the page) interesting. Particularly the lack of information from Powergenix as to discharge end voltage, and some inconsistency as to discharge cycles - 500 as opposed to 200. In the end, it really depends on the application, as with all chemistries. I think NiZN is great for high drain use, such as camera flashes, etc. But for anything low drain, or where reliability is an issue - not a chance! I fear that poor quality control, and a lack of proper documentation / testing has doomed this very promising technology.