The filter does not allow you to drill down into the Custom Objects, we have approx 300 objects this takes considerable time to run for the
Filter on Custom Objects prior to running a comparison similar to Salesforce Change Set, select the required object and fields to compare
Gearset now has support for advanced filtering, prior to kicking off the comparison.
You can select components within an individual metadata type and save that as a common filter for your team to use. You can read more on our blog: https://gearset.com/blog/fine-tune-your-org-comparisons-with-advanced-metadata-filters
Thanks for reporting and I hope you find this useful!
Fred Webster commented
I would extend this to include filters on most metadata types pre-compare. If I know I have 10 pages, 10 classes and 3 objects for a given development effort it would nice to only compare against those.