These gauges are required for playing DBM and DBA. They allow quick and accurate measurement which speeds the game greatly. While experienced players can usually eyeball the tactical movement distance (4"), the circular and radial gauges can help beginners.
The combination of the 40mm linear gauge (called "Big Oklahoma" by our group) and the 1" linear gauge (a.k.a "Small Oklahoma") makes wheeling a unit very easy. Set the 1" linear gauge against the far end of the wheel measuring out from the front base edge how far to move, then place the 40mm guage to form the hypotenuse of the triangle (with the front line an the 1" linear guage forming the rest of the triangle). Once this is set, its a simple matter to move the figure bases to align with the 40mm guage and complete the wheel. That alone is worth the price of the set.
If you play DBA or DBM and don't have one of these sets, you're only making your life harder.