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The protector module that was included in the latest Xoops should work with any of the 2.5 series just fine. You will need to make sure the admin framework is included in your version of xoops but otherwise it should work fine.
Other than the 2.5 admin that was added I believe Trabis also removed the obsolete warning about modifications that needed to be made. Those modifications have been unnecessary since 2.4.5.
The version that is provided with 2.54 seems to be version 3.4. I believe 3.51 was a beta version but you should be able to use it just fine. The big difference is that 3.51 may tell you that you need to do a preload and postload hack which has been unnecessary since 2.4.5. And it will not have the 2.5 admin.
But be aware that as a beta version it could have issues that never were fixed.
I do hope that the features of this module are eventually included in the core as that is the place these belong. (I believe other features should be removed from the core and made into plug ins to make the core lighter and more flexible but things like security items should be built into the core.)
Attending College working towards Bachelors in Software Engineering and Network Security.