If you don't mind me asking, how is that better than a regular microSD card in a holding (captive) socket?
Well I could do that, but the PCB is fully exposed so I don't want to encourage people to try to remove it. If you see a regular microSD card you might try to remove it for whatever reason, or just by 'fiddling' with it, but if you see a soldered down part you just leave it alone. Even with a dab of glue underneath people would still try to take it out. In fact you would think, given it's all exposed, that a card + card holder was used precisely so it can be replaced, which is not the case.
I can buy the SanDisk iNAND parts from arrow.com in the states but their cheapest shipping cost to the UK is nearly $40 (the part costs $6).
And yes I'm using it in SPI mode.