I have and I have to say it is tough. You don´t really get much time to rest between tests all, considering all tests are intense. The speaking part is kind of subjective because you get a human examinator. In my case I got this little old lady, she was grumpy that day so my grades were low. During my prep for the IELTS all my teachers said that my speaking was
impeccable so the only reason I can come along is that the old lady mess my grades.