Having said that, there are also photographic gadgets that do not serve any purpose. Or, to put it this way, they are not even worth their low price. Let's take a look at some of those.
Note: I do include links to Amazon for the convenience of comparison and photos. Personally, I would not use any of the products listed below. But if you think you might have use for them, all the power to you.
Whoever thought of this should be forced to wear it as a hat every day for 6 hours - 8 on weekends. Let's see... Take a low-quality plastic that is a couple of times larger than your camera (try to visualize this folks), and off you go, to explore the magnificent world of the deep. Or, better, leave the camera at the hotel, and enjoy a nice day at the beach instead. Unless of course if you want to look like a disabled person with a ventilator hanging on your chest, and you love blurry pictures that look as if they were taken behind a plastic... oh, wait.
2. It's a Lens! No, It's a Lens Cleaner!
Whoever thought of that had good intentions - don't they all. The idea seems like a good one: take a thing that looks like a lens, which you can mount on your camera. Then press the button, and the powerful (cough cough) fan will make sure to suck all the dust from your sensor. Only, it doesn't. It sucks, but not in the way you'd expect. And spending $140 for something that does a worse job than a $15 cleaning kit isn't very good for your mental health.
3. "Telephoto" Filter/Lens/Whatever
There is also a "wide-angle" thing exactly like that.Basically this is a very fat "filter", which you can screw on your current lens. It usually comes with a 52mm or 55mm thread, precisely because it's aimed at innocent beginners with a 18-55 kit lens. Supposedly, attaching this on top of your 18-55 lens will turn it into a ~ 36-110mm lens. Of course you'll realize that this works as advertised only when focused on infinity. You will also realize that unless you stop down 3 or even 4 stops, you will have ghastly aberrations and softness. Good luck trying to get enough light into the sensor with f/16.
4. Stalker Lens
If you think my title is too harsh, know that Opteka, the company selling this, officially refers to is as a "voyeur lens". This is a tube with a mirror. You attach it on your camera, then you point it forward, but thanks to the mirror you take a photo of something on your side. Ingenious, right? Well, I might be mistaken, but something tells me a tube with a giant hole on its side doesn't make for a very discreet attachment. On top of that, the quality is atrocious.
5. Buffoon Stick
And last but certainly not least, the buffoon stick. Only in our self-centered generation would something like a selfie stick exist. I don't even need to write anything about it, except this: stay the heck away, except if you actually enjoy looking like an idiot in front of famous monuments.