Let me start by saying this security bar does give that initial 'fortress' feeling when installed. The heavy-duty iron construction looks intimidating, and the adjustable length (18.25" to 47.50") means it fits most standard doors in my apartment.
The installation is stupidly simple - just snap the three bars together and wedge it under the doorknob. I particularly love the interchangeable caps system that lets you switch between hinged doors and sliding patio doors in seconds (though sliding door mode reduces max length slightly).
Where this product shines is on hardwood floors. The angled rubber bottom grips like a gecko - I literally couldn't budge my front door when this was properly installed. My neighbor (a 200lb guy) tried forcing it from outside and only succeeded in making enough noise to wake the dead.
However... there are some caveats. The connection points between segments feel slightly flimsy - I can imagine determined intruders might exploit this weakness with enough force. Also, while the rubber foot generally stays put, I did notice it occasionally slips if not perfectly aligned.
For $30 per two-pack, this is decent supplemental security that'll deter opportunistic burglars. Just don't expect it to stop a SWAT team. Pro tip: Combine with an alarm system for maximum protection!