Hi DrDark. I am a little late responding, but I would like to share my experiences. First off, I have not tried eye gaze attached to a tablet, so I can't really compare, but I do depend on my Tobii I-12+ basically 24 hours a day, and I love it.
I was given an older version Tobii by a speech therapist at my ALS clinic as a loaner to start getting use to. I did struggle with that a bit with my progressive lenses, however, with them off, it didn't seem much better. Once Medicare kicked in, we ordered the newest version and the eye tracking is much improved.
Back to your question about lens design, I actually use a progressive designed for computer use most of the time. There is a small section on the top of the lens for distance, and another small zone on the bottom for near. The larger middle section is for intermediate distance or computer distance. It works very well and reduces head tilt and neck pain. My lenses are made by Essilor, but most lens manufacturers have a version. Like what was suggested above, I do use a single vision computer glasses when I am laying in bed with Tobii mounted above me. I can read from my Kindle app and I can let my wife know I am ready to get up in the morning, usually by playing an appropriate song, like “ Friday, I'm in Love”.
Finally, I find there is not much I can't do on my Tobii compared to a tablet or pc. It runs Windows 10. I find the augmented speech program easy to use. The IR is great for controlling the TV and stereo. The other systems may be able to do more, but I am very happy with my Tobii. Good luck with what you decide.