A pen and paper is what I typically use, especially when stuck on a task. But to think about how to timeblock in a way that "works" (I interpret this means, "is effective at keeping one spent on worthwhile tasks), I think the behaviours matter more than the tool (paper/software/or otherwise).

The biggest habits to make time blocking work I see would be:

i) Checking the system (paper/software) regularly)

ii) Capturing all the to-dos, and making sure none are just floating in the mind

iii) Having clear reminders for deadlines and prompts to review tasks that aren't working in a while

When I use a time blocking system well, I'm good at getting lots of tasks done. The biggest obstacles are when a task takes a lot longer than anticipated due to complexity; if I fall behind and don't check the manager; or if I schedule some tasks for someday/far-in-the-future, then forget to review them regularly.

So in short, I think most systems work (with cloud sync and organizational features for software systems as an added luxury), but the biggest obstacle to effectiveness is not checking it enough, often caused by feeling overwhelmed with tasks. Solutions to this include: committing to less, taking breaks, and staying healthy with exercise & sleep for the basics.