In the plugin, you can activate a textblock (some would call it a widget, but it's not widget in WordPress terms) displayed on a single product page. In short terms, you can show up how much a customer could pay per month instead of the full price like this:
Setting this up is quite simple. In the admin panel for the payment methods, each method that supports installments is marked with a dropdown selector with specific durations to choose from. For example, it could look like this:
When no annuity factors is enabled, the dropdown elements is marked red, so it is easy to see which payment and factor that is active. Selecting the bottom most factor dropbox will enable a new factor and the other will switch over to red instead.
Custom text
You could simply create a custom text by going to WordPress internal handler for Pages and create a custom string to show on the annuity factor page.
The principle looks like this:
And will show up on the product like this:
Custom text with filters
If you feel it is way too easy to use a custom page for the annuity factors, you could use the filer rbwc_part_payment_string too. It may possibly be easier to use this IF you have intentions to for example make custom translations on fly.