I was an English major in college. I had more than my fair share of literature classes. As much as I like reading, it was all too much sometimes. Yes, I would read Cliff Notes or some other summary of the book from time to time.
What I've learned is that there is no replacement for reading the book. The same applies to professional knowledge.
There are lots of great resources, some that I use. A great one is GetAbstract. It provides you quality summaries of the books in just a few pages. However, you can't get the true knowledge of the book from a summary. The same applies for articles or research studies. If you find the summary interesting enough to quote or use, read the full thing.
When you read the original, you will understand context that helps you internalize the ideas at a deeper level. It will also expose some things that sound good, but maybe aren't nearly as helpful as you thought.
One example, I read a book - an autobiography - from a very successful businessman. The summary said how it had some incredible stories with great lessons on how to be a good boss. When I read it, I felt like the author was more interested in telling the story about how he met the famous person, and forced a message into it. It totally changed how I read and understood the content.
The message is clear: Read the damn book for yourself.