Actually, the MODERN transfer bar action was invented by.......COLT in 1969.
The "J" frame Colt Trooper Mark III was the first modern application of the transfer bar system, and it was so good, every revolver designed since uses a virtual copy of Colt's design.
Ruger didn't introduce their transfer bar DA revolver until 1970.
Dan Wesson brought theirs out in 1970-'71.
The big advantages of the transfer bar action are:
1. Safety. There is no way a blow to the hammer can break the usual revolver safety blocks and fire the gun, since there is no way the hammer itself can touch the firing pin.
2. A transfer bar action requires little hand fitting during manufacture.
In the older revolvers, a master fitter assembled a revolver by selecting a part and filing and stoning it until it functioned properly.
Hand labor COSTS, and runs the price of the gun up.
In a transfer bar system, the assembler has bins of parts available. He tries parts until he finds one that fits and functions.
This requires MUCH less time.
Colt was the first manufacturer to introduce a revolver that was "machine fitted" in this way.
The disadvantages:
1. Most transfer bar actions use coil springs, and these don't give as good a trigger action as many people like. (S&W alone still uses the old leaf spring in their "K", "L", and "N" frames).
2. Since the trigger controls the transfer bar, and the trigger return spring pulls the bar out of engagement with the hammer and firing pin, the trigger return spring MUST be kept fairly strong.
Again, this limits what can be done with the trigger pull.
3. Transfer bar actions are more sensitive to the strength of hammer strike.
In order to insure reliable ignition, the hammer spring must have more tension than an old style action. Again, the trigger action is stiffer.