Let me mention @Annette to see if she can answer your questions about her project.
From my experience, pressure reducers and filters are only required if you are running micro/misting sprayers that clog with debris easily. It appears this project uses a limited span of tubing, and I wouldn't expect to see a significant drop in pressure at the end of the pipe. You'll notice they've split the tubing and run into two separate lines. This helps alleviate the drop in flow experienced at the end of a long single run.
Re: Ultra cheap and easy irrigation system using an old garden hose
I found my system used to get blocked up with ants. Fix was to put a tap on the end of the line and start it with the tap open to flush the tubing and once it was clear shut it off to have the sprayers work.