First off, the H&R Defender does not fire 9mm Luger. It fires .38 S&W, which is an oddball little cartridge (having a bullet diameter of .361", which is larger than the .38 Special, stuffed into a fairly short case) that started out life as a blackpowder cartridge, and survived the transition to smokeless. Typical loads drive a 158 grain bullet at 767 ft/sec, putting the .38 S&W under the .38 Special.
The H&R Defender was a top-break firearm made in the 1930s and 1940s. As such, it ought to be inspected by a gunsmith for the typical maladies affecting top-break revolvers. Given the vintage, it should be safe to shoot with current-manufacture .38 S&W ammunition (upon blessing by the aforementioned gunsmith.) However, know that the ammunition is somewhat hard to find. As H&R turned out large numbers of these guns, their collector's value is minimal. A gun in 100% condition could fetch ~$300. A gun in average condition can expect to see half that.