If some CF cards work and others don't, it is almost certainly
a symptom of failing to meet the timing specs for the CF standard.
I urge you to check setup and hold times at the CF card interface
to verify that the specs are being met.
When they are met, virtually all CF cards will work fine.
BTW, an Apple II is incapable of using the "high speed" cards
to advantage, so that slower, cheaper cards would be preferred.
Indeed, I also thought it was the timing problem. However, I have not
much I can do to make the timing better since I use ARM on-chip
external memory controller to generate signals for accessing CF card,
USB host controller and on-board SRAM. They all work except some CF
card can't. ARM doesn't allow too flexible signals to be generated and
I don't have any glue logic or spare logic on CPLD to generate better
timing. Since Sandisk is THE leading memory card provider, so I think
it is fine to restrict the use of Sandisk card. CF card isn't really
expensive, a 512M Sandisk Ultra ][ card cost US$15 shipping included.
And you don't really need too many CF card since 512M allows you to
store around 3600 .DSK images, so you probably only need one CF card.
BTW, in BlueFlash, Apple ][ doesn't see CF card, CF card is accessed
directly by ARM and ARM runs at 57MHz, so a fast card does help a lot
in accessing CF card. In my test, to load a .DSK image from CF card to
the on-board SRAM happens almost instantly!