Have you already purchased the Magden M.1b? If not, I recommend that you reconsider buying it. For the price of the "performance computer" you can buy a REAL carputer: screen, motherboard, power supply, everything, which will be a lot more useful, capable, and versatile than the Magden unit. Aside from music, video, GPS, etc., a carputer can also refresh its readings a lot faster than the Magden unit because of software like EvoScan which utilize the SSM protocol (the Accessport probably does too, which is why it refreshes so quickly). The only thing a carputer can't do that the Magden can is integrate aftermarket sensors other than WBO2 (EGT, oil temperature, oil pressure, etc.). However there is someone writing a program to change that now.
If you're set on buying the M.1b, I would not be at all concerned about its refresh rate not "matching" with the zeitronix. You should be concerned about it refreshing too slowly... period. If the OBDII refresh rate is frequent enough not to bother you, I doubt that putting the zeitronix readings next to it will.