Well, Expert Belt only hits on foes you get Super Effective against, so no, you get 20%more with an Expert Belt. You get the same boost as the Choice Items, except, the Choice Items make you use one move forever.
Cons of Expert Belt are that you need a Pokemon that will get you Super Effective or else it is a waste.
Overall with my experience, the Choice Items are better but to stop you occasionally screwing up, Expert Belt can be better in some cases.