I think it worthwhile if you don't already have a couple of bazaars, or like similar buildings either in your city or in your inventory. The 4*5 specialty building is very flexible - gives you the ability to meet daily challenges easily etc. I already have 13 special buildings of varous sizes and ages that allow me to complete most production challenges quickly and still get power, medals, coins, supplies or fps as required daily. If fp production is your only goal then no, SoKs are better but if you are looking for a balanced city that is flexible then they are worth considering