You have a lot of variables for your upgrade scenario, you must consider this before choose OGG:
- Size of your database
- Number of your schemas and objects
- Number of transaction per day
- Some version of OGG doesn't support Clob data types, XML Data Types, etc. You must check this.
- For a full DB synchronization Oracle recommend using Data Guard.
- Even if you fulfill all your requirements with OGG, you have to implement a POC (prof of concept) and test your environment
I think the most important think is the POC, that's when you realize all the issues for your requirements. Also its very important before you pay something for any product to be sure to fulfill all your requirements and its something manageable for your daily basis.