I am new to the forum as well.
Your experience almost echos mine exactly.
I picked up the Memorex at Best Buys for $229 and a $30 rebate. I installed it in an external firewire encloser that used to have an A03. It worked fine.
Then I found the 107 online for $141 + shipping, so I got one. It to is working fine and works fine in my G4/500 AGP, but I will be leaving it in the firewire box.
I returned the memorex today for a refund.
I also bought a memorex 16x dvd-rom drive for my G4 to replace the original. It worked fine. The place that sold the 107, had the 117 for $25, so I ordered that too. I tried the 117 in my G4 and it will not work. They sent me a 2nd unit and it will not work either. I put the memorex back and all is well again.
So for me, the 107 is a keeper as a burner and the memorex is a keeper as a dvd-rom.
Personally, I'd rather have the 107 to make sure the pioneer patches and hacks are fully compatible. but if you can't get the 107 to work...
perhaps you could try another 107, just to make sure it's not the drive.
I ended putting the A03 in my EMachines home computer, and it's working out just fine. This too was an upgrade from the stock CD-R/RW.
Good luck working out your selection.