Are the differences between the different IDE <-> CF converters? Speed? Or are all equally suited for our Amigas?
CompactFlash cards are ATA devices, so most adapters are simply passive devices that adapt an existing connector to the CompactFlash form factor. The primary differences between adapters are the number of connectors and extra frills like mounting kits.
On unexpanded Amigas with IDE/ATA interfaces, you'll need to use a CompactFlash card that supports PIO mode. Most do, but some newer (and less expensive) cards only support DMA modes. When in doubt, check the card's datasheet.