Hi, I am Developer. The speed difference in Most cases, the SD card interface do's not allow the Data to transfer in and out of the SD Card as fast as the CF card. This is compounded by the lake of information for developers to support new products (Products “San Disk”/”Socket Communications” do’s not support for developers code). So SD card may not be the fastest on the market but for Devices that just need Internet connectivity they work grate, but “San Disk” and ”Socket Communications” don’t support any of this platforms (Home automation, Remote telemetry, Chat Clients and Device control in general). The resin they don’t support this markets as there is not enough money in it for them to sell drivers. In fact most of these markets just need Tech support. If you have tried to get tech support for your hand held device they do support, you have probably already fond it to be limiting and in sum cases just useless.