in my campaign, the TAG(P) units are used for Indirect Spotting/Weapons Firing from the Spotter Mech since I've not introduced Arrow-IV systems yet. they are a nice niche device, taking away 1 ton of urge to generate 3-more heat you otherwise can't dispate... O0. i can imagine TAG, using home rules of course, could be Role-Played for artillery hexing as well (the laser verifies the Hex location the shells will land... in 2-3 rounds, give or take the price of Olive Oil...
(P) = Prototype, with all sorts of fun things happening when you roll a 2... ;D