What does Omni Reset actually do?
It purely removes any Batch Activity records and resets the Batch Status.   It does not repair partially posted transactions, but it will make the batch "Available" again.

Can't I just use Batch Recovery instead?
Please do, but Batch Recovery cannot always help as the batch may not have crashed during posting, also it is only available to systems running on SQL Server.  In the situations where Batch Recovery cannot help you have the choice of a huge Techknowledge which cause you to lose information, or fix the problem with a single click in Omni Reset.