At the end of the day concerns are just Ruby modules and they are a core feature of the language. They are an acceptable style of programming. It all depends on the task, your team's size/maturity and the hard boundaries you'd like to enforce.
The problem with concerns is that they can easily start leaking logic into other concerns or models and you've only got your team's conventions and common sense (which are all very soft boundaries) to steer you away from this. As a matter of fact, same goes for Rails engines - they make it very easy to call the parent app from within an engine and it's very tempting to do so at the cost of leaking logic and breaking these boundaries.
If your team can agree and stick to a set of conventions in regards to concerns, there's nothing wrong with using concerns the way Basecamp uses them. If you prefer stricter boundaries, there are other patterns that you can follow (like service objects or ActiveJob or events).
I personally use concerns when the behaviour tends to be very generic ("Paginates", "Cacheable", "SoftDeletes") and service objects for anything that touches the business logic.
The problem with concerns is that they can easily start leaking logic into other concerns or models and you've only got your team's conventions and common sense (which are all very soft boundaries) to steer you away from this. As a matter of fact, same goes for Rails engines - they make it very easy to call the parent app from within an engine and it's very tempting to do so at the cost of leaking logic and breaking these boundaries.
If your team can agree and stick to a set of conventions in regards to concerns, there's nothing wrong with using concerns the way Basecamp uses them. If you prefer stricter boundaries, there are other patterns that you can follow (like service objects or ActiveJob or events).
I personally use concerns when the behaviour tends to be very generic ("Paginates", "Cacheable", "SoftDeletes") and service objects for anything that touches the business logic.