I have used EMS and I do appreciate them, they are a good service and are very reliable for the most part since I'm not going to be silly and say they are completely reliable.
I don't believe that anything is. But they do the job, they do work.
And accordingly to that fact, what I really prefer about EMS is working with them directly after establishing a good relationship with my supplier. Most suppliers from China will offer EMS optional, and it is a good service for that.
But it varies from supplier to supplier, and if you don't have a trust built up with that supplier, I would not bother using the EMS. I'd use something else or ship it to yourself and then ship it on.
This industry depends on the cornerstone of you and your supplier. Every supplier is going to be different, they vary, and some are very bad.
Some are very good, and you want to make a connection with the very good ones, and keep them. Help them out and help yourself, that's the key I guess to the game.