by Old Tom, of old-tom.com
Here's a riding crop from JT's Stockroom (TheStockRoom.com, formerly named JT Toys):
Here's a good picture of a quirt from U.S. Wings.com:
It's the second from the bottom of the page.
A quirt - at least, the ones I have seen - is relatively short. Roughly half is handle, and half is the whip. The handle might be wooden, or might be leather and flexible. A quirt has two or three relatively wide blades. The ones I have seen have all been rawhide.
With a quirt, the whole thing is flexible and floppy. A riding crop, by comparison, is stiff.
The cane, because it is so flexible and whippy, can be difficult to land accurately. (I consider this a feature.) Picture an area the size of a thumbtack. To hit that area - and ONLY that area - with a cane, requires a fair degree of expertise, and not everyone has that.
A riding crop, on the other hand, is stiff. It's easy to control and use. If you can handle a hairbrush, you can handle a riding crop.
Even though it's stiff, it *is* still thin and whippy like a cane. That means you can be careful, and that also means you can create some interesting - ah - effects.
One style is to have only the slapper strike the target. You can do a very rapid slap-slap-slap, perhaps gently and perhaps not.
Because the stiffness of the crop allows you to be accurate, you can take a *swipe* at the target. Instead of slapping *on* the breast, you can swipe across the nipple, for a very nice effect. (I also enjoy removing clothespins with the riding crop.)
Like with the cane, you can slap-slap-slap the riding crop anywhere and everywhere.
You *can* use the crop for full strokes across the bottom, just like with a cane. The effect is fairly similar, especially with a longer crop, and you need to take similar precautions - be careful about wrapping, cutting the skin, striking too high, etc. I personally don't use the crop that way except for variety's sake. Whatever I can do with a crop, I can do better with a cane. (That is, whatever I can do with full strokes of a crop, I can do better by using the cane.)
What makes a crop a crop, is the slapper. Different crops will produce different effects. Crops can be *very* effective, and can be especially effective in those hard-to-reach places.