The Megastek MT90X is a very compact lightweight tracker suitable for most dogs and some larger cats.
It has the following features
Good battery life - with optional pet modes enabled (one to three days)
Audio monitoring capability
On/off switches on tracker
Unique command set - limits application options to manage it.
Small size limits GPS/GSM signal in poor reception areas.
Note - all these trackers have a tendency to fall to the underside of the collar which means they can sometimes lose GPS signal when operating in poor signal areas - For all but the smallest animals this can be eased by placing a small weight at the opposite end of the collar. This will counterbalance the trackers weight and encourage it to stay where it has a better view of the sky.