Gotta chime in here, folks...
Yes, I am a pediatrician.
This is not a bad device, and you are not likely to be able to get in far enough to perforate your kids eardrum, but do be careful! (Ear canals are really sensitive, and easy to scratch)
As noted above, a diagnosis of an acute ear infection that needs antibiotics should be made by someone who knows what they are looking at (e.g. a medical professional). The diagnosis depends on seeing PUS behind the eardrum - not a red eardrum, not clear fluid behind it, but the yucky thick white stuff that indicates an active infection with bacteria. Lots of ear infections are viral, and lots of ears can hurt without the presence of pus.
There are new evidence-based guidelines that recently came out regarding prescribing antibiotics, and in general antibiotics are way overused for "ear infections".
That all said - if you see a red drum, it's likely ok to watch it (unless your child is acting really sick, then ALWAYS get thee to a medical provider, please).
If you see pus, (note the lovely picture of a bulging ear drum someone posted above), your child *may* warrant antibiotics, but may also warrant watchful waiting or a "just in case" prescription.
If you see drainage from a perforation, your kid needs antibiotics. (But don't panic - ear drums nearly always heal beautifully, and it does not mean that you waited too long... sometimes it just happens, and it might happen fast).
I've got the super expensive one that I've had since med school, and I'm still considering this! The battery alone for my real one is nearly as expensive as one of these...