Lap Monitor requires you to place the counter on the inside of the track pointing out to count laps down the straight... need to be careful not to place it in a spot that is prone to getting hit from lap traffic. The timing system is limited to cell phone and not easy to export results for public sharing for a group setting.

Trackmate is better for a group of drivers with a nicer software package for exporting race results online, etc.

I have both systems and it's nice to pack the Lap Monitor when I travel to a track for open practice without their timing loop on... if I'm going to host my own event in a parking lot or backyard track then I use Trackmate.