I like these.  I used to practice occasionally with alphebetical sentences.  They are unnatural, but tend to give a good workout.  Going back to 'regular' text after a hard exercise can make them feel easier.  I know you need to practice punctuation, but too many initial caps really used to bother me.  I'd practice by copying text from books, and they felt overloaded with punctuation.  Amphetype never gave me meaningful stats as my errors were largely detected at the start of sentences.  Punctuation's a drag.  Some of it could be auto-calculated in your editor.  I still hate simultaneous key presses.

Ooh, that's a lot of fun, thanks for pointing it out!

I've been thinking about teaching strategies, too. Most lessons seem to start with the index and middle fingers (STNE) and then add ring and pinky.

I've been building my own lessons, which I'll share if they seem to work - I started instead with the left hand (ARST) and then add the right-hand one letter at a time. My rationale is that starting with four fingers of one hand feels really easy. It feels more like a game, and you don't need to think about ergonomics. It's lazy and casual. So it makes a good first online lesson for someone thinking, "I don't know if I really care enough to commit to this." By the time the second hand comes in and you actually have to sit in a proper touch-typing position, you're already committed. So the mental barrier to getting started just feels lower to me.

However, I'm already thinking about an alternate approach: start instead with the right hand (NEIO), plus all the letters that haven't moved from their QWERTY locations. That means that by the end of the very first lesson, users can type half the alphabet! Of course, it's mostly the less popular half - but you get to complete sentences much faster - you can type phrases like "View a moon above an ocean in New Mexico" in the very first lesson! 3 lessons later you've brought in the whole left hand home row, and now 3/4 of the letters in English, by frequency, are done! And the remaining letters aren't "leftovers" like Z and X, they're common letters, so even though you're getting bored and losing steam, the later lessons each feel like a worthwhile accomplishment.

What about ASETNIOP? http://asetniop.com/
Only 10 buttons, one for each finger. ASET Shift Space NIOP. Shift+Space=Enter. Other letters are pressed with combinations. Ex: N+I=H.

That's why my amphetype fork has options to ignore case and automatically fill in punctuation.

Asset lessons start as you proposed. Home row is ASET DH NIOR, and first lesson uses ASET to form words: "assets sat at seats. a seat sets state estates at sea. stats assess as tests at ease.". Then it adds D. Sometimes it may remove some letters. http://millikeys.sourceforge.net/asset/demo.html