Looks like the
FireBoard S1G is using a 900 MHz radio frequency while the ThermoWorks RFX is using 433 MHz. Similar concept, indeed, though the lower 433 MHz frequency should have a better penetration through metal enclosures. Both should have better penetration capability than the Bluetooth 2.4 GHz signal.
Now, the problem I have with 433 MHz is that it is smack in the middle of the amateur radio 70 CM band and I worry a little about radio frequency interference between the probe and my radio gear. I am a ham radio operator. We’ll see.