In BTD4, the Mortar Tower was only priced $2000 (medium) excluding the ability. In BTD5, the Artillary Battery (same as Mortar Battery) was priced $9000 (medium) with the ability. The Pop & Awe Ability lasted 5 seconds, and all non-MOAB-bloons on screen were stunned. If you subtract the price of the Mortar Battery/Artillary Battery with the ability, the ability would cost $7000 alone. Is this price worth the ability? (Note: this is just an opinion-wise discussion.)
It does stun blimps. I think its worth it, especially on freeplay.
Plus, a 2/3 mortar costs around $3,000 (on BMC), so the triple shot should be $9,000 including previous upgrades. $9,000 minus the $3,000 gives $6,000 for the firerate increase and $3,000 for the ability.