I have both (one EZ Flash IV & two M3 SD Perfect). If you want Real Time Save and the Real Time Clock, then go with the M3 Perfect. I got it from shop01media.com for roughly $74 shipped (currency conversion and $10 shipping charge). The EZ Flash IV is a nice little card that you can get from dealextreme.com for $24.
I love my M3 Perfect but you can't beat the price on the EZ Flash IV. Also, it's GBA cart sized so it won't stick out like the M3 SD Perfect.