eFlash is a ZIII card, so if you plan to use it in a ZII system, it won't work.
KickFlash seems more attractive though, as supposedly there's a way of making it work with BlizKick modules. This would be useful when using a BlizKick incompatible accelerator card, however yet still being able to use BlizKick's features. I still need someone to confirm that this feature actually works and I would gladly buy a KickFlash card.