That might be a bated question, asked by Mr Z, to see how many would fall for it. Or maybe Mr Z is that confused by the basics of training. Or maybe a combo of both, who really knows. See not too many jumped to answer that since 12-19-13 and Mr Z appears to have vanished all together.
As far as reps go:
20 reps can do for you what 5 reps can't. And 5 reps can do for you what 20 reps can't. In other word, you have to experiment with reps and sets to find what will give your the best results in the shortest amount of time. 20 reps can build muscle mass, as well as 5 reps, just have to spend a little time to find what works for your individual body type.
Try not being influenced by Mr Big Balls of 2013 (or any other "champ"), and what he may suggest or do in any of his video's. Or the gym "expert" who seems to know all the answers. Also including me (no expert by any means) or any one else on GB. Take any advise, or new idea, and approach with caution at first. Try a new program for a good 6 to 7 weeks, the first 2 weeks are more of a breaking in period, getting accustomed to the change in exercise style, etc. If results seem good, than you get an idea of how your body responds to that type of workout. If no, or poor, results...than try something different.
Going to failure, for a BB'er, is really never needed. And may even halt progress for some. If wishing to try experimenting with that, and other different methods, that help yourself. You will only find out the results by doing it on yourself.
K.I.S.S. (Keep It Simple Stupid) might be a good motto to keep in mind when planning any future workout. I know I do. Good Luck