There's absolutely nothing wrong with Elbox products and I have loads of them.
However, the statements above about getting Poseidon to work with the Spider are correct (good luck finding it), which is why I installed a Deneb in my A4000 (installing the software takes a couple of minutes as an older version is on the ROM and you just set a jumper, boot and then install it from Workbench - no disks necessary, and then let it update itself when you get online). You also get the FlashROM funtion which also comes in handy.
My Mediator takes care of my Radion 256MB card (providing extra system RAM) and a Sound Blaster 128. I intend to get arround to fitting my PCI Catweasle at some point as the OpenPCI stack is supposed to have drivers for it and will run alongside Poseidon.
Now that Poseidon has been released for free, I'm surprised that Elbox haven't created their own version for download.