How tough? Do the different substrates make any difference?

Generally, after drying, the crack-free tape could be easily removed from the substrate. The thick casting can be difficult due to non-uniform drying conditions.

Here are difficulties with thinner casting. I guess the polymers stick to the substrates or the ceramics particle sizes are too large/not dispersed well.

In my opinion PTFE, Teflon substrates can be used because of the bad adhesion of rubber to fluoroplastic polymers. Also, substrates should have small roughness.

Try to use DTF transfer film. In my experience, it is even easier to peel off compared to Silicon coated PET film.