The software alters Mail's email retrieval process for IMAP accounts.
While IMAPCheck does its job well, it's important to note that it still does not enable rules support on IMAP accounts. Though this bundle makes it possible for Mail.app to see new email arriving in these folders, it doesn't process any rules associated with them. Implementing rules support would require more development and testing time than the creator has available at present.
One other important consideration is that while IMAPCheck is not particularly complex, it still alters the behavior of some of Mail.app's code. As a result, there is some risk inherent in modifying another application at runtime. It's possible that using IMAPCheck could negatively impact Mail.app, corrupt data, or cause other unforeseen issues. As always, it's wise to proceed with caution and make sure that you have a backup in place before using any software that modifies another app.
In terms of compatibility, IMAPCheck was written and tested against Apple's Mail.app version 2.1.1 on 10.4.8 with all the latest updates as of Dec 10, 2006. The bundle has been tested on multiple MacBook Pros and a PPC Mac Mini, and is a universal application that should work on other versions of OS X. However, it's worth noting that the further away you get from version 2.1.1 of Mail.app, the more likely you are to encounter issues or crashes. The creator strongly recommends updating to take advantage of IMAPCheck's features.
Version 1.2: N/A