The bottleneck is comprehension though. Most speed reading techniques don't cover it. Learn to visualize and grasp concepts quickly.
Speed reading also helps a lot in comprehension in that if you can skim the entire book you've already understood the gist of what the book is about.
Just don't expect to read books much faster. The best books should be read slowly. If you're reading one book a day, you should question whether that book was worth reading.
If you want something free, google Tim Ferriss's speed reading tips. They're easy to understand and get started with.
However, it seems to have made me very good at skimming and picking topics off a page. I can identify the one or two Google results I want to follow at half a glance, while people whom I know to be capable of reading at twice my speed are still reading through each headline separately.
And I can run my eyes down a wall of tutorial text to pick out a couple key terms that identify the section I want to read in depth.
In short: it didn't deliver the benefits promised, but that doesn't mean it was without any benefits.
I do it unintentionally. Probably because of how I learned to read. I also have very fast recognition of stuff so probably that is the reason. I am of course faster when I am reading novels and stuff, but I must say that 'visualization part' which you have while reading fiction is gone with me. I just scan and understand, and try to learn what happens next instead of creating a scene of that page etc.
Perhaps if the goal of reading is to identify specific information anywhere within a text quickly and move on to something else or switch to reading more mindfully at that point, then it may make sense. Personally, I read exclusively to obtain information and retain it. If I don't care to retain the information, I won't read it in the first place. So not being able to retain anything meaningful save for the few instances I slowed down ended up defeating the purpose for me. Lastly IIRC, I once read about the neuroscience of reading with regards to speed reading and the gist of the article ended up saying that it takes discrete periods literally measurable in observable time in order to form memories, and speed reading feeds in information continuously at a rate that does not allow for this crystallization to occur--because the actual reading is like a blocking operation neurologically to memory formation. When we read normally, we pause and reflect in various abstract ways on the information which creates connections and hence memories.
Without learning the visualize first, people usually end up drinking from a firehose - they don't have the capacity to absorb the information. The human brain is designed to comprehend images, not words. So to go high speed, you have to make a habit of visualizing the words.