I do use an oral digi for my family.(Actually I have two of them- one for inner ear readings and a seperate one for oral readings)
As far as accuracy? I did take my lil girl's temp with it and had it read different from the doc's reading. Could have been due to the fact the the meds kicked in before we got to his office or because I had to take her outside in dead of winter.
If I recall...they use the underarm method for VERY young babies and tots? May not be as accurate and takes longer too? I think I recall reading that somewhere once.....