Firstly I will say it is inexpensive & does block out light, also you can blink/open eyes with it on, but I have to say, it's not overly comfortable, I sleep on my side alot and it really digs into my face & is a little bit harder than I hoped. Also I left it under my pillow one night I didn't wear it & there was a sleep mask shape purple mark on my sheets in the morning! (Colour had transferred)
In saying all of this, it's one of the better ones that I have tried, but could be improved.

Bought this sleep mask for my husband. Have bought from Boots and other shops before and, compared to those ones, this is the best sleep mask bought so far. The adjustable straps make a big difference.