Cradlepoint MBR1400 vs IBR600B reliability?

I'm looking for passthrough WAN with very reliable failover+failback to 4g/LTE (modem must LPE/firmware flashable to any major US carrier)

Besides form factor and gig-E passthrough on the MBR1400 and the IBR600B being 10/100, are there any real differences between the two? I see that the MBR1400 modem is a USB attachment versus directly integrated. Will that affect reliability?

Thanks