A word of warning on these things. The part that plugs into the Agnus chip is a little daughterboard that will probably interfere with you being able to plug the derringer back in. I have one of the megi-mini boards and while it did indeed give my 500 2mb of chip RAM, I lost the ability to use my Spirit Memory board which plugs into the CPU slot like the derringer does. The version I have uses the gary chip for that extra wire (via an additional socket).
I will eventually take out the megi-mini board and put a 1mb Agnus in its place and have .5mb Chip, 2mb Fast but keep the ability to boot PAL. I'm not sure what good 2mb of chip RAM is in a 500 anyway.
