I live, work, hunt, hike, boat, camp, &tc. in a state with a baker's dozen variety of rattlesnakes, and other venomous reptiles (and arthropods), encountering them frequently, and have yet to find myself in a situation that could be improved by being armed with any handgun with snakeshot, or for that matter, any situation that could be improved by shooting a snake with any sort of projectile. The only advantage afforded by shot vs. bullets is the somewhat diminished risk of rebounding projectiles, but this is in actuality a moot point, inasmuch as if you've got time to draw and aim a gun, you can, in half the time, take one step away from the reptile, eliminating any further risk.
I hear tales of water moccasins in boats, and if this were a genuine risk, I suppose I'd rather shoot #9 shot than even a .22 solid into the bottom of a boat, but apart from that scenario, I think the whole snakeshot-as-snake-defense thing is the product of unreasonable, unwitting fear, and creative, exploitative marketing.
Most all the likely dangers to be encountered outdoors are apt to require more potent projectiles...