You get a superior experience. 2.552 with Pestalence's package does not enable widescreen resolutions nor does it enable multiplayer Dynaverse. The 2.552 version also has moronic point defense, with Ph3's and PhG's routinely fired at range 15 for an average damage of 0.16 per pulse assuming no ECM shift. The AI in 2.552 fires suicide overload Fusion Beams at ranges that cannot do any damage. This was fixed in 2.564 as well as other bugs, such as Mirak hit and run pause button.
The Mod Chooser in Pestalence's pack never worked in Windows 7, so that's no loss to me.
But if 2.552 is what a player prefers, it'll always be there. Nobody is required to play 2.564.