pretty much to put it simply, pacemaker are a known and proven brand, also i think the xforce exhaust systems have put a few people off buying the brand, have you heard an xforce catback next to a decent catback system? theres a reason xforce is cheaper than the rest.
X Force are cheap Chinese copies. Major brands do their own R&D on extractors and design them from scratch, X Force take an existing extractor and make a jig from those and then copy them. They change something minor as to not infringe on patents but they are essentially just a cheap knock off using lesser quality material. They look nice and shiny but they use thinner pipework and flanges.