Modifier keys suck on traditional keyboards.
Modifier keys are great when they are put under your thumbs.
Modifier keys are great when they are put under your thumbs.
The thumb (and thumb knuckle) keys are my favorite design point, but the entire design is excellent. They are out of stock, but the designs are open source, and there are a lot of other great DIY designs around.
The Ergodox has thumb clusters similar to the Kinesis Advantage. There is also the Dactyl, and many many more.
If you want to go down this rabbit hole, reddit is a good place to start: https://www.reddit.com/r/ErgoMechKeyboards/