Why is it listed as class 11/10? Should it just be singular and class 11?

Doke lists "advantage (=benefit), use" as a second meaning. In this case, the plural does make sense. Can you confirm these meanings?

No I guess those meanings must be obsolete now. I realise Ye Olde Doke lists the plural, however note that both Scholars English-Zulu (Dent & Nyembezi) and Compact Zulu Dictionary give only a singular

Anyway ... My understanding is that there is no longer a plural izinsizo

Just to add to the confusion after lengthy discussion I now understand there is a separate word insiza, izinsiza (9/10) meaning resource or aid, e.g., izinsizu kufundisa "teaching aids" BUT I don't that noun in ANY of my dictionaries

aaargh !! why didn't I opt for German, or Russian, or Urdu?

Oh yes I remember why now