I'm not a big fan of camera straps. I have, but in general I don't like having my camera dangling around my neck. That's what makes the Spider Black Widow holster an appealing alternative.
The basic Black Widow includes the holster and one pin. The pin screws into your camera's tripod mount and the holster threads onto your belt. Slide the head of the pin into the holster's slot until you hear a click and your camera is secured.
The Black Widow holster when used with your own belt is designed for cameras up to 2 pounds. From 2 to 4 pounds, Spider recommends using its $15.99 belt that can be combined with an $8.99 belt pad. If your gear weighs more than that, you'll want to step up to Spider Holster's Pro system. I tested the Black Widow holster on my regular leather belt with a Nikon D7000 and its kit lens as well as a few full-size megazooms and I never felt uncomfortable from the weight.
There is, however, the slight hurdle of feeling like a bit of a dork for hanging a camera from your belt. Sure, it's convenient, but as my wife said the first time I used it, "fanny packs are convenient, too, but I'd still make fun of you for wearing one." She then refused to stand near me while I wore it. I did get a lot of stares whenever I used it, but that might have just been curiosity or because people are used to seeing cameras on straps and not slung from someone's hip. Speaking of, depending on the size of your hips and your camera, this holster might be awkward to use.
Again, though, it is convenient because you just drop your camera in and it stays in one spot, and it's just as easy to release it and start shooting. There's no swinging around as it would with a strap, so it allows you to move more freely and faster. It also made it very easy to change lenses. Plus, I frequently carry a camera with my small children around, and having it on my hip keeps it from smacking them when I bend over and out of the way should I have to pick one of them up. Also, it's a lot more difficult to steal a camera attached to your belt than it is on a neck strap.
The complaints I have with the Black Widow are with the red latching piece and the pin. I'm sure the latch is designed to hold up to heavy use, but the handle wiggles around in the holster. It just feels flimsy and for the $50 price of the holster, it really shouldn't.
With the pin, you're supposed to lock it down into your camera's tripod mount with a wrench. However, if you do that it means you're stuck with it in there until you go get a wrench to remove it. If you just hand-tighten it to avoid this, you'll just end up screwing it back in all the time or risk losing it.
This is really sort of a nonsense complaint because I suppose most people aren't going to take it on and off a lot, they'll just buy extra pins for other cameras/camcorders or buy the tripod plate. But, if you have a smaller camera and/or you don't use a tripod with a quick-release plate, you'll need to grab a wrench to free up your tripod mount to, you know, use a tripod.
Lastly, the price seems somewhat steep for what you're getting. I mean, it feels overall well-constructed, but for amateurs and enthusiasts, $50 is a lot to cough up. But, if you're looking for another way to carry your camera then a neck strap or sling, and still want fast access and security, this holster is definitely an option worth considering.