Some will refer to that hammer design as the "Fish Hook". Never quite understood why as, at least to me, it doesn't resemble a fish hook. It was the first "High Speed" hammer design used until the early 50s, when it was replaced by a semi-target style hammer spur. Nothing is unique about it, it's just a typical pre-Model 10. There should be no concerns about using +P ammo with it, although I don't understand why anyone would want to use it instead of regular standard velocity ammo for typical recreational shooting. Truth is that +P ammo is only marginally more powerful than standard ammo, mainly it just uses a lighter bullet at a little higher MV.

Regarding "Transitional," that is a term I will not use as it is essentially undefined and meaningless. As an unofficial description of yours, every collector knows what "pre-Model 10" means.