I never recommend any professional software to anyone when I have something better to share. Yes, you heard me right here. I'm talking about the manual trick which requires no paid utility, You just need to have Outlook client with a sound knowledge. No worries if you don't! I would like to share a blog post here in which you can read how to remove duplicate items from Outlook PST files.
Copy and paste this URL to your web browser: wordpress.semnaitik.com/2015/05/07/remove-outlook-duplicates/
When you can do this manually, why would you spend money on a paid utility? Think about it.
Thanks and best regards.