Re: fortiextender vs cradlepoint
The key difference is the logical 3G/4G or 5G interface with FortiExtender lives in the FGT, while it's just IP next hope with Cradlepoint or any other wireless router, unless you set "IP Path-through" on those wireless router.
It's not a big deal if the wireless device pulls a private IP (NATed by wireless carrier's device inside their cloud). But if you order a static IP, which provides a static public IP from the carrier to the wireless device that might make a difference. Sometimes work or break. Also depending on the model of Cradlepoint (I believe at least cheaper models), their NAT support only one inside subnet configured on the LAN interface. So if you come from behind FGT without NAT at the FGT, it couldn't browse the internet via wireless.