I suspect this all boils down to commercial factors for the carrier, and this is triggered via the the amout of data you download.
If you are in the top few percentile of all plan users you will absolutely draw attention to yourself. I tend to believe that these sorts of scans are only performed against top abusers. Like small credit card fraud there is a an accepted cost built in because the cost of surveillance and correction can be much higher that the cost of the fraud itself.
If you just use a common about of data you may never have any issue becasue it takes resources to track and manage abusers, and if that user is within an average user profile it actually works against the carrier to cut you off because its just revenue.
As I said, the router’s WWAN IMEI is a bit like a MAC address that is bound to a hardware brand and type. But unlike simple MAC spoofing, you cant bypass that without some very advanced spy level hack skills and that’s can even be a criminal offence in some countries. (IMEI numbers are involved in network and cell tower authentication.) The carrier expects a link with a device that has the IMEI of a voice handset - and the Netgear cant do this.
Your carrier might work with the Netgear just fine, but that will only due to how motivated the carrier is to dectect and police this breach of their terms. You can buy the Netgear, but there is a risk that you’ll get cut. The only way to defeat this reliably is via the method I’ve given you, which is akin to exploiting a technical loophole.