How to help 7 year old getting "hayrake" appliance

Hello. My seven-year-old son is getting a "hayrake" dental appliance on Friday as he has been unable to stop sucking his thumb. He'll wear the device gor six months.

How uncomfortable will the procedure be? Will he have to eat soft foods for a while? How long will it take for his speech to adjust (he's already in speech therapy)? Any ideas on how to make this process easier for him?

School doesn't start until early September so at least he'll have a few weeks to adjust.