Will this GiveWP Add-On slow down my site?

Absolutely not. The plugin will only do its stuff for logged-in Administrator, and optionally a few things for other Give-specific user roles who have certain permissions.

The regular visitors will not see, or “feel” this Add-On plugin! Even a registered “Donor” basic user account won’t see or “feel” this plugin at all — it won’t even load in these scenarios.

Again, this plugin does not load anything for visitors of your site. It does not do anything for logged-in users who have no sufficient permissions.

To use the benefits of this plugin you need sufficient permissions – which only come with Administrator user roles (of course) or any of the higher level GiveWP-specific user roles. And even then the plugin tries to leave as less footprint as possible!