SD is slower than CF, even on a humble A600! Believe me, I tested out. But the device + a few micro SD cards are obscenely cheaper than 2Gb (and over) CF cards.
Shame the design of the device is not suitable to reach the SD from outside the Amiga.
On a PCMCIA reader (the same 5-in-1 people have here) micro-SD cards freezes both my PCMCIA Amigas (600 & 1200). I use a 128Mb Memory Stick or an old 64Mb CF for transfers (or wireless Ethernet).