Yes they need the Vernier sensors.
The temperature sensor can be found with a mini-USB plus and is not very epensive.
But the magnetic sensors for the compass are quite expensive, and you need 2 of them.
Moreover, they have a proprietary plug, meaning that you have to get either the TI-Nspire LabStation Cradle, either the Vernier Easy Link to plug them on your Nspire.
The LabStation is allmost as exensive as a TI-Nspire, which seems normal when we know that it does include a modified TI-Nspire motherboard.