Blackout curtains are sold at almost all home improvement stores and any number of additional companies and stores as well. While all curtains do a decent job, there are only a few models which operate inside of tracks for 100% room light control without any cracks to let stray light into the room.
I'm not able to cleanly get to the link you provided, but I'm sure that they are just fine if they are rated for 100% light blockage (blackout).
I have inexpensive curtains in one of my rooms and they do a good job of fully blocking the light coming in. Since they are curtains, light still comes through around the edges. I would need additional shades in tracks to completely block the light.
So, while this completely blocks light, you can see that light still comes in around the edges...https://thewirecutter.com/wp-content/uploads/2018/04/blackout-shades-lowres-5726.jpg
Compare it to this which helps to seal the edges...https://www.amazon.com/blackout-Sleepy-Time-Tracks-eliminates/dp/B01M0AJNLP?th=1
Or this which is a roller shade designed to use a track at the sides and bottom for perfect light control...http://www.bbsedona.net/vision/Boxed-Motorized-Hotel-Blackout-Blinds-With-Side-Track.jpg
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