Yes, it is. Yes, the mods are worth it. I personally use all the court mods (the original courts is really terrible for me). Yes i think some modders use AdFly and something like that (understandable, of course), but there's some who's not, and their mod is really really good.
I reccomend taking a look at iamSamke 'A Complete Guide to an Improved NBA 2K17' for reference. He list all the mods that are available right now and categorize them (like courts, draft class, cyberfaces, etc)
viewtopic.php?f=225&t=102294For me personally, i use Lagoa's courts
viewtopic.php?f=225&t=102321 (he makes a really great courts), maumau78 SFX mod
viewtopic.php?f=225&t=102610 (changing the sfx of the ball hitting the rim, the swish sound, etc), and exrxixxx custom NBA TV scoreboards
viewtopic.php?f=225&t=102620Those three are my favorite mods, and they don't use AdFly for their mod. You can download them at NLSC download databases or at mediafire.
I think i can't imagine playing the game without the use of mods now