Hardie Plank Pros and Cons
Maintenance is the same as any exterior painted surface and will need to be repainted periodically. How often it needs painted will depend on the grade of paint used and the number and thickness of the coats.
Hardiplank siding is far superior to the Masonite or hardboard siding it was meant to replace.
Don't look for meaningful insulation gains in any type of siding. If you need insulation, install it in the wall cavity between the studs (such as R-13 fiberglass batts) or skin over the outside of the wall with 1" styrofoam or urethane board (R-7) before applying new siding.
Anything that is painted will eventually need to be re-painted. Under like conditions, Hardie-plank will hold paint as much as twice as long as wood. If you want no maintenance for 30 years, install masonry and don't paint it.
Don't look for meaningful insulation values in any type of siding. If you need insulation, add it to the cavity between the wall studs (with products such as fiberglass batts or blown-in insulations with a R value of 13 or more) or "skin" over the outside of the walls with 1" insulation panels (such as urethane or styrofoam with a R value of 7 or more). A lot of contorted hype accompanies products and their R values. Be careful!
In my experiences, paint holds at least twice as long on hardie-plank as it does on wood. If you want NO maintenance for 30 years, install masonry and don't paint it.