I actually stumbled upon a sibling to this typewriter in a thrift store today. Not the exact model, but very close.
I pulled a key and checked. It has a coiled spring over membrane. The slider is integrated into the keycap, so not compatible with any mechanical switches that I know of.
The key action is linear and light with short throw. Creaky on off-centre key presses.
Nice texture on the keys though: gritty without being coarse.
