On the plus side, with the working iFlash CF card, I've found the SIDE works in all of the 8-bit Ataris I've tested it in so far, including a rather temperamental 800XE which won't normally load anything above standard SIO speeds.
So far I've confirmed it working in my 800XL (The ONLY ONE the MyIDE+Flash will work with), a 65XE, 130XE and the 800XE.
With the cross-system reliability (sadly missing from my MyIDE+Flash cartridge) and the RTC, I think we're onto a winner!