Pros: -just insert a sim card with credit (the sim must be unlocked; means without pin) then turn it on and use.
-it will additionally display to the gps coordinates the velocity.
-overall built is not too bad.
-you can store 3 phone numbers that can be dialed.
-earphones are included.

Cons: -too cheap. (I have bought it when it was about 200$; now it is 150$).:-(
-sometimes it has some difficulties to get gps signal. In such a case go to an open place to get better signal.

Other Thoughts: You can find more informations about this gsm/gps tracker on: http://www.tzonedigital.com/newEbiz1/EbizPortalFG/portal/html/products.html#

Bottomline: nice to have something like that.
Imagine you are lonly in a deep forest an you do not find the way out. Just send somebody your coordinates and he will help you to get out. or in an emergency case. you have an accident in the mountains and can not move. you can send the right coordinates where you are.

Pros: I own two of these GPS trackers and I use them to hook them up to my two cats when they are going outside. The device is quite small and although my cats are both quite small, they do not seem to be bothered too much by carrying the GPS tracker around, probably the weight of this device is quite low.
The reception is excellent: it still works, even when the device is tilted when the cat lays down. Although not water-proof, small amounts of rain do not get in and the cats dislike of water makes sure it never gets soaked.
Putting in a cheap SIM card makes it work and when a cat is not yet home when its getting dark, I can easily retrieve him sending an sms and looking up the coordinates on Google maps.

Cons: It is expensive, but still less expensive than similar devices elsewhere. Furthermore, the only way of configuring it is by sending an sms with a code, costing you one sms from your cell and one sms from the prepaid card in the device (for confirmation).

Other Thoughts:

Bottomline: Very usefull device if you want to be able to check on your pet when its not home. Saves you sleepless nights and posters all over the neighbourhood.

Pros: Just pop in a sim-card (that is not locked with a pincode) and turn it on. Within seconds it will have a GPS fix and GSM connection and you're ready to go.

Call the tracker's phonenumber (without hiding your caller-id of course) and let it "ring" a few times untill you get the busy signal. A few seconds later it will send an SMS back to the caller with the GPS coordinates.

It has three buttons that can be used to send coordinates and/or make a phone call to pre-programmed phone numbers. With the headset you can actually make calls with "ok" sound quality. Ideal for kids or emergencies.

With coordinates via SMS'es tracking is near "live", but with GPRS it can be really live at a much lower cost.

GPS reception is really good. When you're inside you only have to stand close to the window for about 10 seconds and the device has a fix. If you don't have armored concrete ceilings or live in a metal cage you'll even have good reception inside.

Overall build-quality is good (sturdy casing)

Cons: As far as I know you can only configure the tracker by sending SMS'es, the USB port is only used for charging.

The battery can only be replaced by opening the device, which is covered with a warranty sticker.

To set up GPRS tracking you'll need to use an external service to collect data. I'm still figuring out how to get GPRS to work.

Other Thoughts: It shouldn't be too hard to configure a webserver to receive the GRPS data from the tracker and use it to display the location on google-maps or google-earth.

Mine came with an "american" USB power adapter instead of the displayed "european" adapter.

There was no manual, I downloaded mine from the manufacturer's website:
http://www.tzonedigital.com/eng/products.asp?id=93

When I get GPRS to communicate with my own webserver and can plot maps, I'll send one of these with extra batteries by mail to a friend in Australia... just to see where it went.

Bottomline: If you want your kid(s) to be able to call home without giving them a cell-phone you could give them this. They'll only be able to call up to three pre-programmed numbers and you'll be able to track their location.

If you want to protect cars, trucks, cargo or anything else from theft you could hide one of these (and wire it to a bigger power source).