Yes. Necessary to have repetition to learn a language
Yes. It works. By the end, German words and phrases have been burned into your brain.
If you buy this Part 1, don't bother with Part 2, and perhaps 3 and 4 as well. Part 2 is a repeat of what was learned in Part 1. Although once you buy Part I you do not need to buy the other Parts, I was disappointed that I could not continue on in the series and learn more vocabulary. Instead, I had to switch to another language system.