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This mod is designed to enhance tactical capabilities (making combat more thoughtful), speed up development times, and so on. In other words, it's a rework of the gameplay as envisioned by the author (Nargott) to get the most out of it.
Mod 5.5 changes the gameplay to a lesser extent, but it includes many other changes. New hero classes, new artifacts, and new objects on the map have been added, etc. We also have a presence for this mod on the website:
/topic/11565/
In short, just my opinion (which may differ from the opinions of the mod authors): if you are interested in PvE, then that mod looks more promising. If PvP, then definitely this one.