Just to add my bit.
iDM don’t officially support their SIMs in routers, they only support compatible mobile phones. But that doesn’t mean it won’t work and what you’d need to do once you move to iD is insert that SIM into a phone to set up the account and app. Then once the online account and app are working you should then be able to pop that SIM into the router.
I wasn’t aware iDM did a data only SIM but yes you can use one of their unlimited calls and text deals with how much data you need.
They've currently got an unlimited everything SIMO on a 24month deal for £16per month.