Follow the specs
If the maxmum size boat for the pole you are considering is 25 feet and your boat is 31 feet, don't buy it. The compression loads on a whisker pole can be enormous. For yur boat, the minimum size whould be the LC10-18 (Forespar). And at that size the line control pole makes a lot of sense. These things are heavy and the less wrestling you have to do the better. Ours is an LC13-24. It's a bear to manage single handed. Don't forget a peoper setup on the mast, too. You will need a car and track and control lines. And if you can arrange a topping luift, so much the better. his is not extending the boathook to hold the sail out.