The library is licensed by the BSD 3-Clause "New" or "Revised" License. While this hasn't been tried in court, having such a license would make it very difficult for FinancialForce to force you to either pay up or stop using that particular version. There shouldn't be any issue using any source code under this license for any practical reason.
As far as dependencies go, once you have copied the source code, you own that particular copy of the source code. The dependencies are your own, and you can manage those however you'd like. For example, the BSD license allows you to modify the software in any way you see fit, so you can choose to fix problems, remove unused code, add more features, etc.
The only restriction you need to be sure to follow is to mention that parts of your product contain BSD licensed code in the documentation for your product. In this case, it would likely be sufficient to have something similar to the following in your documentation:
Open Source Libraries
The following libraries are used by this application.
By doing so, you're providing a link to the source code and its licensing terms, which should satisfy the clause. You might want to ask a more specific question on properly crediting OSS on Open Source.