I've often considered the question of whether physical or digital books are the better option.

Although I do really love having a library and actually holding a book, the following factors swing it towards digital for me:

1. Convenience - instant delivery and the ability to carry as many books as I like with me on my kindle and phone.
2. Cheaper.
3. Environmentally friendly.

I never really considered the reading speed and comprehension argument because I never felt like it was an effect for me. I can understand how it would be for some people.

I think, in the end, it comes purely down to personal preference. For kids, though, less screen time and fewer possible distractions is the better option.