I don’t know, but I would’ve think so. Part of the reason is that almost no one actually learns to read this stuff fluently without using the key and going letter by letter. So getting any significant sample of people to test it on would probably be hard
I can’t read (or write) it without the key, however I’m quite fast if I get to do it. I have thought of trying to learn it completely, mainly to see how hard it would be and what I’d learn (apart from, you know, learning brädgårdschiffer) from learning a “new” alfabet. I’d be interested to see how I view it in comparison to regular Latin script. I speak somewhere between 2 and 4 languages depending on how you count and I’ve found every new one interesting and insightful to learn so it would be fun to see if learning to read a new script fluently would be anywhere near as insightful. Ultimately I’d like to learn Korean or Chinese but that be a major challenge and take a lot of time (also, I could probably not squeeze it in to my formal education with the path I’m going to take so I’d have to do it in my free time)