Hiii and
The probe under the UTH between it and the tank is for a thermostat, which is pretty necessary and will regulate your UTH. While the one under the substrate is sort of a double check for what the temps are on that side of the glass.
I love my baby BP (6 months old ish) but the other guys are right it does take quite a bit to keep the husbandry OK sometimes. I enjoy her quite a bit and she is much more chill than any corns I have held (but I have never owned one so maybe they were just uncomfortable with me IDK). Mine is currently in a 20 gallon long, but will need to be upgraded either to a suitable rack or a min of a 40 gal tank eventually. But some babies are too uncomfortable in big tanks to just start out that way. Sorry if too much info for meow and my. Welcome to the BP bug!