I think it is only worthwhile if it can be run off your vehicle's battery with internal batteries as a backup. I will guarantee that if you always have to charge it, it won't be charged when the bke gets taken. I suppose you could use the USB cable as a charging source, but now you also have to hide wherever your plugging the USB cable into.
Most inexpensive live trackers are just cell phones. In the not too distant past, some private investigators use to attach GPS enabled cell phones to target's cars to track them. These type of trackers are basically the same, but there is a variety of functionality (some will just send gps points, others can message to alert to movement or low battery or enter/exit a geozone.). What the product you listed didn't mention (or I didn't see it) is how much it costs to maintain. Since it is a cell phone, it always needs service. You also need to consider if the GPS data will be logged. So that if power is lost or the tracker is found, the data was logged and you can find the last known location.
For instance, one device we occasionally use is here: http://www.trackingtheworld.com/wtgprs.htm
. I'm not sure the cost of it (probably $2-300), but you can see they charge $60/month for the service. I don't really know a lot about civilian/commercial trackers and their cost, but I don't really think there is a cheap solution. So unless you have a $10K bike, it may not be worth it.
You might look into buying a cheap prepay phone (with GPS capability) and just keep it on your bike. Short of that, I think any type of live tracking is probably going to cost $500+ when you start adding in service. But like I said, I don't know much about commercial trackers.