is it good to use on hardi plank siding>

Yes, the OSI QUAD Sealant is suitable for this use/application. Just make sure the siding surfaces are clean, dry, and free on contaminants including any cement fiber dust and that any bare edges are sealed with a primer/paint. However, keep in mind that James Hardie does recommend the OSI QUAD MAX sealant on their siding as the better alternative.