TOMORROW: TODAY:
Just tapping into the directory (6700 books) takes +10 seconds. Extract and cache book information (after clicking through ~5 dialogs) took 1h 16m.
(It is nice that there's ongoing a progress dialog. It indicates that most of the books were not cached, so apparently the collection arrange did not cache books, but some books were alread cached.)
After caching everything, sorting by title or author in the file browser took ~15s. Sorting by date modified took ~11s.
In contrast, just opening the directory (from clicking into it or leaving a book) takes about the same 10s, so I assume it's running the same logic.
Going back to the connected Collection: Opening the collection took ~10s, while set to sort by title. Switching to author sort and then back to title was <2s each.
So clearly caching the metadata helps a lot.
However, now I have to look at what happens when books are updated. That's the entire reason I went to KOReader from Kobo native. I update books on my reader several times a day.
Opening the directory again after USB connect/update/disconnect took 1m 11s while set to sort by date modified. And metadata changes to books previously cached was updated until I manually requested it to update for those books. KOReader user guide seems to indicate it only updates when requested.
Opening the connected collection again was basically the same as before. ~10s to open, shows previously cached data, even if changed during update.
In conclusion:
Connected Collections, once metadata has been cached, probably work fine for most users. Sorry for disparaging the feature.
Not ideal for my user pattern, but I'm still learning.