Well, I understand that you know they aren't a great SD weapon, as even 95% of hardcore mall ninja's are smart enough to know that would be dumb, lol.
To answer your question directly from my own personal experience, yes, they are kind of junky. Fun, potentially effective on small game, but ultimately kind of junky.
The one that I had was purchased at Big 5. Made in China, mostly plastic. It had reasonably effective (adjustable!)sights, though they weren't particularly sturdy and broke almost immediately, necessitating repair by super-glue. Past that, it worked pretty well, but there just wasn't anything that inspired any particular confidence in the overall design. The safety, in particular, was a little sketchy. It worked, and the basic principle of why it worked was pretty obvious, but a lack of anything approaching smooth operation always left me a little wary that I was going to twang my fingers or something. It never happened, but it goes back to that confidence thing.
As far as actually shooting it, the adjustability of the sights actually worked well enough to get me on target most times. The bolts left the pistol with a fair amount of zing (I actually would have liked to chrono them out of curiosity), and they would hit to point of aim, more or less. The cocking mechanism was a bit awkward, but it did work very well.
If you have some spare cash laying around, and you can find one on sale like I did, you will probably get your money's worth in entertainment out of it, which is more than I can say about a lot of things. If your looking for something serious and useful, probably best to pass.
If your looking for something to quietly whack small pests in the backyard with, I honestly recommend a blowgun. With very little practice, you can be accurate enough to kill stuff and your neighbors will never know. You can pick up a decent blowgun and enough darts to last you for a good while for under 20 bucks.