Daniel Naroditsky recommended using this to improve at tactics but I was wondering if it was in any way worse than using a book with tactics for example.
Its a fairly subjective question but their "learning" area is solid, the tactics tool is good for learning pattern recognition quickly. Most sites (lichess etc) have similar functionality.
Regarding how effective it is. Its dependent on you. If you learn better by doing. Probably better, if you like theory than book.