I'm trying to acquire the reflex of installing it on each newly created app on Heroku. Knowing how painful it is to setup automated backups on your own (and even more painful when you don't and end up needing it), it's really great that you can have up to one month retention for free.
It came really handy on one of my previous projects when I needed to investigate on data loss that occurred a few weeks back.
Definitely a must install if you're using PG on Heroku !
It's definitely an improvement on the previous cron add-on, however I have encountered more than once issues with the UI trying to manually launch a task ; the job output never showed up in the browser and I ended up with an error message that didn't really make sense and wouldn't go away.
This add-on has been superseded by the Heroku Scheduler add-on which allows to manage the tasks with a web UI.
I used this add-on on a project last summer to benchmark and optimize various implementations of an application. It was quite efficient and worked well overall. Definitely beats writing your own injection framework.
However I thought it was lacking tooling in terms of reporting and aggregation of the stress test runs ; I had to maintain a worksheet of the various runs to keep track of the results. Maybe they have improved in that area since then.
It's nice that you can change plans just for one day and keep control of your expenses (although it gets quite expensive pretty quick, but I guess none of the services of this kind are cheap).