The Mac App Store does not allow developers to sell plug-ins at this time. The Antares edition of SoundSoap includes the plug-ins for FCPX, Logic X and other compatible plug-in host applications, but the Mac App Store edition does not. Mac App Store apps are not allowed to run third-party code, and since SoundSoap uses a well-respected third-party MP3 encoder, the Mac App Store edition does not allow MP3 encoding. For these reasons, the Mac App Store edition is priced lower. Contact Antares if you wish to purchase a cross-grade from your Mac App Store SoundSoap to the Antares edition.
The Mac App Store also does not offer flexibility on pricing, so be aware that purchases made at the Mac App Store may not be eligible for upgrade pricing unless Apple offers this capability to developers in the future. Antares edition customers are provided a significant discount on major version updates.