We've added a new template tag to Buttondown's automation engine: {% random_number a b %}, which generates a random number between a and b.
You can use it like this:
{% load random_numbers %}{% random_number 0 1 as number %}{% if number %}[Click this link](https://google.com?utm_source=a){% else %}[Smash this link](https://google.com?utm_source=b){% endif %}
Buttondown is the last email platform you’ll switch to.