I wouldn't say it's too big for reading a book. As someone who temporarily owned both the 12.9 and 11 back in 2018, it's all in how you plan to hold/use it. I tell people visualize your use cases. Will you be sitting mostly? Do you you see yourself walking around with it in one hand with a cup of coffee in the other? This may sound funny, but will you use it on the toilet? I say if you're going to be carrying it and using it a lot, the 11 inch is the better buy in my opinion. It operates as a handheld tablet better due to it's smaller size and dimensions. If most of your use case is at a desk or you'll mostly be sitting with it resting on something, the 12.9 is fine and you get the benefit of the bigger screen.
My general advice is, if you own a MacBook or any laptop, get the 11. If you don't have a laptop or you're looking to replace a laptop, I would go for the 12.9. For me I chose the 11 because for as long as I can only do Plex Server and Emulators on MacOS or Windows, I will always own a MacBook. I know some will say you can just get an iMac or Mac Mini for Plex use, but I prefer a Laptop because I value flexibility even in my main computer. There are times that I will carry both my Laptop and iPad on trips, another advantage I might add for the 11 inch in that it adds less weight to this combo. Mostly, I use my iPad in mobility scenarios and my Laptop stationary and for serious productivity. The 11 for me is better for walking around with my tablet which I love to do, for using in bed, and for taking notes while standing and holding. The 11 fits in more tight spaces. For example, I work from home and use my iPad and MacBook while working from my company issued Laptop and Monitor. My iPad sits right under my monitor perfectly as you can see in my picture. The 12.9 would block the screen. This may not be big for many, but it's a big deal for me. I use my iPad for TV/News while I'm working. I love it right below my work monitor in my line of sight
. Fyi, that's as high as my monitor will raise. It's like it was made for the 11
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