If you use them with finesse then no, not all spurs work the same by any stretch. In fact, depending on how picky you are, two people of varying heights or leg proportions can’t switch spurs, and even the same person may need different spurs depending on the barrel shape and sensitivity of different horses.
The width of the spur band will determine how stable it is on your boot. Some may need an auxilliary strap or heel chain that goes straight down from the spur tight under the heel, in order to prevent the spur from riding up.
I posted this photo in another thread, and you can see how it really needs a heel strap or heel chain (which had broken before these were taken) to sit level:
http://www.easphotography.com/Tindur/IMG_1501.PNG
The angle which the spur shank comes out of the heel band is important as well. These are generally rise shanks, straight shanks, or drop shanks. If you hear someone call a spur a “quarter drop”, for example, it generally means that the pin through the spur rowel is set a 1/4" below the centerline of the band which goes around the foot.
How much drop etc you need is set by your individual leg conformation compared to your horse’s barrel shape, how well you control your leg, how sensitive your horse is, and the size of the rowel itself.
I ride a wide barrelled horse and have long legs, so I could ideally do with a rise shank. To get around this with the shank style I like, I have a rather large rowel. The point where you first contact the horse is generally at the top of the spur rowel, so a drop shank with a large rowel can act like a rise shank with a small rowel. It’s the relationship between the top of the rowel and the heel band.
The rowels themselves determine the “severity” of the spur. Lots of points act almost like a smooth wheel, which means that fewer points are “shaper” by virtue of less contact area. The pointedness of the points themselves is also a factor. Like a spade bit, western spurs with big rowels and lots of points are often thought severe, where they’re FAR more soft in action then a single pointed english spur…especially if they’re used properly and rolled rather than jabbed.
Yet another factor is the length of the shank itself (how close the rowel pin is to the back of the boot). If this distance is short, you generally have to move your leg a long way to activate the spur.
So, as always, it depends. You should pick a spur that lets you touch your horse without tension coming into your thigh, at the minimum.
The straps themselves are fashion. You’d only go wrong if it was too short or too long to cinch down properly.
Last thing - you can choose to order most with or without jinglebobs. They’re a nice metronome to some, and incredibly annoying to others. I love em, personally.