We've upgraded our existing comparison filter in several ways to improve the usability and feature set.

Accessing the metadata comparison filter

The fastest and easiest way to open the new comparison filter is to simply click on the cog icon shortcut from the new sidebar when in Comparison filter mode:

You can also access managing your custom filters via the comparison filter dropdown:

Building a new comparison filter

Building a completely new filter is easy. Simply:

Select the None (0) option, which will clear any existing metadata type selections.
Pick and choose the metadata type(s) you want to add to your filter
Choose if you want to always include any items for a type to be included in future comparisons, or specify specific named items based on the current items found between the two orgs
Add any custom rules using regex or specific object names that will also be applied as part of your filter
If you wish to save your current selects and rules as a permanent filter for future use, click Save filter... to give it a name and save the configuration.
Note: you can also apply a filter to your current comparison without saving it for permanent use.
Once you select Save filter..., leave the default option to Save your changes as new filter ticked.
Then choose a 'Name' to your filter, and decide if you'd like to Share filter with team. Once done, select Save filter.

Below is a quick video to demonstrate the process of creating a new filter.

Custom metadata filters can be shared with your team

When you save a custom metadata filter, you can choose whether to share it with the rest of your team or if you want to make the filter private (available only to you).

Who can edit a filter shared with the team?

When a filter is shared with the team, only its original creator or a team owner can edit and save changes to it. Team members can use the filter but cannot make and save changes to it; they can use Save as to save any changes they make and save it as a newly named filter.

Custom filters (private and shared) will appear in your filter menu in the My filters section. You can find them here as you would with the Gearset standard filters:

Updating an existing filter using manage custom filters

To edit a pre-existing filter via the manage custom filters panel:

Open the Manage custom filters settings
Choose your comparison filter from the drop-down
Add/remove types or specify rules and items that you wish to change for your current filter
To apply the filter without making permanent changes to it, simply click Update comparison filter.
Note: This will update the filter only for the comparison you're running.
To save the changes and update the existing filter, click Save filter... and choose the applicable option: Update the filter with any changes you have made.

Below is a quick video to demonstrate the process of updating an existing filter (to which we've added a new metadata type named Apex test suite).

Updating metadata types on a filter selected for already run comparison

If you need to quickly add new metadata type(s) to your current view from the comparison results, you can simply use the +COMPARE shortcut from the list of types in the sidebar to add it to an already selected filter.

To permanently save the change, you can do that via the manage custom filters panel.