I just checked out the critical reasoning 300 questions and there are a couple of issues with this document.
1) It contains a mixture of official questions and unofficial questions with no sources given. Some questions may be much better than others and there is no way for the non-expert to tell which is which.
2) Only 1 solution is given for each problem and the name of the expert who offered the solution is not there. Therefore you do not get two if the things than make Beat the GMAT great, a full discussion from members and experts and the name of the person whose explanation you are reading.
3) No additional information is provided such as difficulty, etc. For example, the Veritas Prep question bank free and available at
https://www.veritasprep.com/gmat-question-bank/ gives you the percentile of the question and shows you what other people have chosen for answers and how long they have taken. Even the official GMATPrep pack add-on "Prep Pack 1" sorts questions into easy medium and difficult.
With that said, it is 300 questions that someone has taken the time to gather and select the answers to. So you would not be wasting your time if you do these!
Have fun!
David
