The 66-2 has the advantage in that it does not have the internal lock, nor does it have a "MIM" hammer or trigger. The only reason I stay away from guns with the internal lock is because the lock hurts the guns desirability at resale time. There are some who just won't buy a gun with a lock, therefore should you decide to sell the gun somewhere down the road, the pool of potential buyers is smaller. Apparently there have been instances where the internal lock caused the gun to "lock up". Certainly not what you would want in a self defense gun. The same holds true for the "MIM" Metal Injection Molded trigger and hammer. While I have not heard any first hand reports of these parts actually failing, some people believe these parts are inferior to the forged hammer and trigger. If I were in your position, I would opt for the 66-2.