I use an Armstrong 6" diagonal cutter to cut hard tacks and they wear out quickly. Which Klein tools cutters do you recommend for this application?

You can use the D252-6 6" All-Purpose Diagonal Cutting Pliers are induction heated and for tougher applications.

The Journeyman J2000-59 Heavy-Duty Diagonal-Cut Pliers are the most durable for this application because they have a beefier head and optimized cutting angle. They are 9" long, however.