As I mentioned before, I worked Hotel Security some years back and I have always have a soft spot for the security of people traveling. Hotel doors look and feel strong, but they are far from that as one hard push can break them open easily.
I cannot make claims about the quality of this particular device, but by my experience the principle is very sound:
It is portable and sold for under $30, so if it is strong enough, it is cheap security for when you travel.
I’ve seen the doorjammer, it works, and if I traveled I’d have one. Pro Tip: practice with it at home. A Lot. If you’re in a strange environment – like a hotel room – and things go sideways your habit will be to “grab knob and pull” which won’t open the door. Your human brain will know there’s a blocking device at the floor but your monkey brain under the stress of getting out won’t remember it because removing the blocking device is not a trained procedure and will be a unique requirement used only on very rare occasion.