Unlimited access to all learning material for a flat monthly subscription fee. Unlimited = read all*; Unlimited+ = read and practice all*. Certification need payments per course.
Personalized practice typically follows a loop: assess your current skill level, give targeted questions, learn from your answers, and schedule review so you retain what you learned.
Most effective systems follow a loop like this.
The system should respond to your mistakes, not just your time spent.
If it keeps giving you the same difficulty regardless of performance, it’s not truly adaptive.