The nice idea behind a task manager with time blocking is that you have a central place to check your tasks and progress. What do I do now? Should I check the next calendar item or check my todo app? Both? Nah, not gonna happen.
The main issue is that while there are apps that try to tackle this, they either fail on being too basic for tasks (for example, Fantastical) or being to weak managing calendars (for example, Butleroy). Perhaps is because the coding effort is double for both approaches and it is difficult to one developer to crack both nuts. Best one I’ve seen is Amazing Marvin, but it has a totally non-appleish user interface,