I have a presence tag device (because it came with the kit) and the small size is nice; it easily hangs onto a keychain. However design is a tradeoff of features. Interrelated parameters with the tag device include battery size, battery life, how frequent it wakes up to contact the hub. The shipping device represents once choice of the combinations. It is small, so to get a decent battery life the time between wakeups to check if it can contact the hub must be set to a relatively large number of seconds. I don’t know about other people, but I find that when I arrive home the tag usually fails to notify the hub it is present before I open a door.
I think there is a market for a larger-sized tag that is rechargable so that it could consume more battery power per period of time. In turn that would allow it to have a stronger signal, letting it be detected at a longer distance or more reliably at a short distance. And the wakeup period could be short. An example application would be in a car. A tag that woke up every few seconds would actually work the way the demo on the Smartthings site show, quickly telling the hub the car is home in time for all the wonderful events to happen.