jeepguy:
$450 is a good price for an excellent condition 2nd hand Model 66.
Yes it is not a good idea to use high velocity light weight magnum ammunition in them (125 grain being the most commonly cited)as it can cause cracking of the forcing cone or flame cutting of the top strap. This is why S&W developed the model 686 which has a more robust forcing cone and top strap. Although more durable the 686 is also heavier and does not balance as well for many shooters.
For your purposes, loaded with .38 special or 158 grain magnum rounds it should last you years, mine dates to 1973 and has required a tune up twice.
The key lock means the gun is a 66-6, dating from 2002 to 2005. Many people consider the keylock to be the spawn of Satan, there have been rare instances of it failing and locking up the gun, but I personally wouldn't worry much about that.
Short summary, it should be a fine gun for your purposes, download the how to check out a revolver sticky at the top of this forum, check out each one, the one in best condition is the one that I would buy.