I used their service twice and i am disapointed.
On the first song i didn't like the mastering quality.It saw only louder and a little brighter.
On the second song was the same story.I tried to get my money back and it was not possible.
Now i get it.Music is personal and it is made by humans for the humans.
I found out that mixing and mastering ,nowdays,is a lot cheaper that in was 20 years ago
So i payed 20 or 25 $ for a real mastering and Voila.I got what i wanted a master that not only sound louder but is deeper sweeter,creamier.
I found on fiverr website a very good engineer called cata 546 and after this themixbros.com a dedicated studio for this.I am very impressed not only by the quality but also that i was able to tell the engineers what i was after and also they even advised me a little bit on the mixing aspects of music.