Currently, tripwire flare is pretty lackluster because the vision don't really benefit Soviet army much when most of their stuff works best at close range and the long range unit can spot for themselves (SU-85, ISU).
You underestimate the power of vision. Extra vision is so much more than just letting your maxims fire 5 range further. Flare trip mines can tell you what is coming your way and from what direction. It allows you to turn your maxims and AT-guns in the right direction so they can fire the moment something is in range. Having early vision prevents you from getting caught off guard by a flanking attack. It allows you to get your units into optimal cover before the battle starts.
The best part is that it can be placed by all your non-support infantry, which means you don't have to rely on a single combat engineer squad to run around and place them everywhere. Within a few seconds of a territorial victory, you can have every flank covered with some trip mines to prepare yourself for the counter attack.