these are not against the tos it is player sided like your boosting the graphics you see as the player not for others to see, Also I have used enb's for Skyrim the elder scrolls for a while and there is nothing wrong with using it they are just heavy on the frame rates. It is not something that alters the game and or files or does not give the player and edge and is not a bad or hacking tool it is something that every pc can use.
For me I don't use it because my graphics card has been getting too hot and I will need to get thermal paste or replace it soon.