A number of Tactics Ogre fans will tell you that the PSP version, whether vanilla or with the One Vision mod, is superior to the recent Reborn PC release. Each version has its pluses and minuses, so it’s largely a matter of taste. The port itself was fine on release, despite the recent trend of SQEX PC ports that were messy on release but were fixed later (like Chrono Trigger and Cross).
Yes, it’s a light remaster of the 2005 release. Seems to be part of a larger effort on Falcom’s part to get their older games more accessible on newer hardware. Players have needed a PC to have access to their catalog.