Tried Gelli printing this week. It's harder than it looks, but still very easy compared to other types of monoprint. You do have to work very fast with regular acrylics, even if adding extender. The acrylic still dries quickly and might tear the paper if you're using very cheap bond and aren't pulling if off fast enough. But like the other kinds of monoprint, every print you pull is a surprise and the medium seems to do a lot of the work of painting for you.
Denise Fleming used Gelli print for her new book This is the Nest That Robin Built. Her text is wonderful, as always. More about it here.
I took Gelli Plate Printing: Mixed-media Monoprinting Without A Press by Joan Bess out of the library and found it useful. There are masses of Gelli print videos on youtube, but I find they either go by too fast or are too chatty and slow. The book was helpful for me to try one method at a time.