The Price of Freedom, weird little oddity that it is, was designed in many respects as a response to the first edition of Twilight: 2000. Both games have some important parallels: they both attempt realistic takes at a somewhat fanciful political/military scenario, said scenario setting up the assumed starting point of play for the player characters, and said scenario also making it necessary for characters to take a survivalist attitude.
This is a bit of a niche model for running an RPG, but equally it’s not altogether surprising that someone should have looked to Twilight: 2000 to see if they could mimic its success. For make no mistake about it: the first edition of the game was a huge hit. Marc Miller’s Far Future Enterprises, inheritor of the GDW legacy, offer some evidence for this: their guide to the product line includes, amongst a wealth of useful data, figures on how many of each product were printed, which tends to track reasonably closely to sales levels (since products which did not sell did not require so much in the way of reprints). The core set of 1st edition Twilight: 2000 had some 97,518 copies produced.
This is incredibly healthy by tabletop RPG standards – it’s not D&D levels, but very few games reach that order of magnitude, and by comparison GDW produced just shy of 250,000 copies of the Classic Traveller core rules when you add the various different formats they sold them on. When you consider that Traveller was the top-flight science fiction RPG of the era until it was eventually overthrown by Cyberpunk and Star Wars, it’s clear that there’s strong evidence for the contention that Twilight: 2000 was the market leader in the military RPG niche – and to a large extent it was that niche, with more or less no other attempt at a military or postapocalyptic tabletop RPG approaching its success.