Most spearos start out with scuba fins just due to having them on hand probably. I know that was my reason. The long blade on a freedive fin will require you to kick less which will conserve your oxygen. If you're just starting out don't worry about it though. Be safe and have fun.
You'll be fine starting out. No problem. The longer fins use. A longer slower kick to keep respiration down. But I will tell you to get some free dive fins and try scuba with them. I use mine for scuba and will never go back to regular fins