Cable People: Are splitters really unidirectional?

Most cable splitters are like this one with labels for “In” and “Out”. Are they diode protected and thus unidirectional, or are they actually bidirectional? I want to use one in a non-conventional fashion to help reduce cable clutter. I want the external feed to go into one of the two “Out” connections, and want to route the “In” from the splitter to my TV Cable Box and the other “Out” along the living room wall in the opposite direction, under the threshold, and into my office where it connects to my Internet Cable Modem.

I know I could just test and see if it works. But my wife is sleeping to TV right now, and if the set suddenly goes off from my testing she’ll wake up and rave on for a half hour about how thoughtless I was to interrupt “her program”. So I figured I’d just ask all the cable gals and cable guys here.