I also have a Trangia stove, which I some times use for day trips because you can carry it all fueled up and ready to go, leaving the fuel bottle at home. Many backpackers are looking for the lightest weight stove they can possibly find. The cost of the stove is usually a secondary consideration, if it comes into the decision making process at all.
Take a look at the statistics on the efficiency of the penny stove vs the competition given on the link provided:
http://www.jureystudio.com/pennystove/#2 and click on the heading "Independent Tests" if they do not come up with the link.
The Trangia has to be primed and brought up to pressure before cooking on it can begin, but it is not a bad stove at all. At one time they were a standard issue item for every Swedish Army recruit. With the Penny Stove you get a blue flame on ignition, so you can start cooking on a Penny Stove as soon as it is lit. Many alcohol stove designs require the use of a priming pan. The Penny stove does not, and it is much more wind resistant than the Trangia and most of the other designs out there are.
True, the Penny Stove is not as durable as the Trangia stove is. But it is more than durable enough for most of us. So far I have not had any problems with damaging any of my backpacking stoves, regardless of type or make. I believe stove choice is more a matter of personal preference than it has anything to do with functional issues. There are plenty of backpacking stoves out there on the market that will get the job done more than well enough.