Mr Jones,
Several months ago I tinkered a bit with HOLTEK HT1621.
I encountered some "traps for young-players" I would like to make you aware of:
1. Clock speed - in case of 3V3 operation, the clock speed must be reduced below 150kHz in WRITE mode and below 75kHz in READ mode, otherwise the driver chip remains unresponsive.
2. Writing a command code requires 13-bits long word to be sent to the chip and in block write mode a 9-bits long command/address word needs to be sent prior the data. This may render SPI module in your system controller useless for this task and may force you to write an appropriate bit-banging code (which happened in my case).
Hope this will shorten your "time to public"
Apart of these, HT162x is an excellent choice and it is cheap as a dirt and that prevails.