[glowing12131]

Is "Non-IP Data Delivery" (basically SMS but for raw data packets, bound to a pre-defined application server) already a thing in practice?

In theory, you get all the power saving that the cellular network stack has to offer without having to maintain a connection. While on protocol layer NIDD is almost handled like an SMS (paging, connectionless), it is not routed through a telephony core (and hence sloooow). The base station / core will directly forward it to your predefined application server.

[vv_]

It has been heavily advertised, but its support is inconsistent. If you are deploying devices across multiple regions, you likely want them to function the same way everywhere.