Colt 03s,and I own several, were probably the most popular carry pistol before concealed carry really became common. This pistol is another ingenious design and is still a viable weapon today even though the design is over 100 years old. The Colt 03 along with the Remington 51 cited above were probably the best of the American produced pocket pistols of the 20th Century and either could be an effective weapon today.
However,given a choice, I would opt for one of the newer designs as I wouldn't want to stake my life on a pistol that if human would be eligible to collect Social Security.
I'm going to try and take this thread back to the hobby we love and make a point here. I have no problem hunting with and shooting 100+ year old shotguns and that's the reason many post here. However I don't have to stake my life on the performance of these wonderful weapons of a bygone era and the criteria for a defensive handguns has to be and is quite different than it was in the last Century.
Jim