I love factions and always enjoy including various organizations and groups in my campaign settings. It's generally a good idea.
I think the DMG advice falls apart in the "perks" section. Most of the rest of the advice is good, but as presented renown is kinda unneeded as ranks are merely cosmetic and could be hand-waved. What is really needed in the subsystem is good examples of perks, but the book doesn't provide any. There's no starting point or guides to balance against.
Even the Adventurer's League - the place where factions see the most attention - doesn't have any examples of perks. Ranks are kinda useless except for downtime day unlocks at Rank 3. They're not even finished since they're saving ranks 4 and 5 for when high level adventures are released, but they've released 30 adventures and Rage of Demons is coming right up, they should expand beyond level 10 any time now.
I wouldn't want to have to create a whole perk subsystem or examples, as that's beyond my free time at the moment. But that's something I'd love to read. Someone should totally pitch that for En5ider. Generic organizations with perks. Easy money.