Hello,
I had set an aggressive schedule to complete course work in MCD Level 1 (Mule 4) and appear for certification. My main source of prep was MCD Level 1 (Mule 4) material with certfun questions as an additional source. It would not be an understatement to state that certfun was critical for me getting certified.
Its format allows you to practice in the exam format. Personally I liked the mini-format as it allowed me to practice in chunks as against spending 3 hours.
I would highly recommend including in your preparation as it will significantly improve your shot at getting certified. Wishing you all good luck.
Thanks