I’ve tested the Trackimo 3G and both versions of the Marco Polo (RC and pet) using Phantoms and Mavics...they both have their pros and cons.
The Trackimo is a bit big for the Spark and can present some mounting challenges as previously mentioned...if you live in the USA do NOT buy the (cheaper) 2G version as that technology is being phased out by cell phone companies. The sellers of 2G units don’t really disclose that to people in America.
In any event you must be operating in an area with compatible cell coverage.
One additional benefit of the Trackimo 3G is it also has a BlueTooth transmitter that can be activated when you get close to zero in on the drone.
The Marco Polo RC unit is the smallest, lightest tracker with 1-2 mile range, does not require cell coverage/connection and has the handheld tracking unit. It is very accurate and easy to use. No subscription, ever. One handheld can be paired with up to 3 transmitters.
The pet version is larger than the RC variant but very weather-resistant.