ETim,
the link you have posted is the tracker I have for my motorbike. When I go on holiday I leave it in the pannier overnight. The pannier is a locked case and the GPS works fine from within.
It comes with 2 batteries and you need 2 because the battery life once charged is about 12 hours. There is no way of attaching it to a cycle apart from the strong magnet which is built in.
In my opinion the money would be better spent on getting really good locks for a cycle. My little GPS has lots of really good features on it and serves its purpose for holidays.
The other disadvantage of that rear light GPS tracker is that it appears that a lot of ebikes come with a fitted rear light and so an extra light would stand out too much.
Steve