I just bought a Pro 100M Wireless Shutter Remote Control Release fits Nikon D90, D3100, D5000, D7000 Digital Cameras from Amazon supplied by BV-electronics for £13.99 delivered.
I have a Nikon D3100.
Ordered Sunday night and arrived Wednesday morning.
Arrived in small mail lite bag (which would have fitted through my letterbox) and then a double lined box (inner card) with bubble wrap around the transmitter and receiver separately.
There are no instructions but I don't think any are required.
The receiver battery (CR 2 lithium 3V) was wrapped in blue plastic which obviously needed to be removed as the positive terminal was covered. Battery easily fitted to receiver. It has a small on/off switch but still obvious as without it the battery would run out when not in use (unlike the transmitter which has a button to operate). It is obvious when the receiver is on as a red LED flashes around once a second. Bottom of the receiver is a fitment to fit to your hotshoe (which also contains a thread like the one on the bottom of the camera for a tripod) which fits onto the top of the camera but obstructs the pop up flash (so just let it dangle) - this only fits one way around. There is also a 2 position button to operate the camera from the receiver without the transmitter. The connection to the camera is via the top socket labelled gps and is tight and only fits one way around (as the socket has rounded edges on one side). It is relatively easy to insert but needed a lot of force to remove.
The transmitter has one push button like the one on your camera (part down focus, full down shutter) and a 2 position switch to switch between taking the photo immediately or delaying for around 3 seconds. It is around 6cm * 3cm * 1cm. When you part press the transmitter down the LED on the receiver changes to a solid green.
Both transmitter and receiver have 4 tiny switches (covered in brown plastic) which I presume set the frequency. I haven't changed them but I did try moving one and it seemed to require pushing a pin through the brown plastic.
The distance seems to be pretty good. I walked out my patio door, closed it and easily took photos from 30 yards away. I didn't go any further - this was fine for me as I doubt I'll be further than 10 yards away.
I only have 3 small criticisms (none of which would put me off buying it):
a) the fitment to the camera is tight, especially when removing it.
b) the transmitter button stands out a bit so if you were not careful packing it you could leave it with the button pressed in which would discharge the battery.
c) when the battery in the transmitter run out you'll need a very small watchmakers cross hair screwdriver to take it apart and fit a new battery (there are 4 screws).