I've used mikrotik with USB 4G dongles and with mini PCI e cards. What I've found is they are ludicrously stable with the mini PCI e cards and quite the opposite with USB dongles. I was using a USB dongle for quite a while and it would require frequent usb power cycles. On the weekend I was using one that would hardly last an hour before needing a full power cycle. On the flip side I've had a mini PCIe one up a pole in the heat of the sun running faultlessly for a year.
Anyway, my question is does everyone else find the same thing? Is USB simply a poor solution or have some people got it working well? I have used it with both Optus and Telstra USB dongles. If it's been working well which dongle have you been using?