The much smaller "fills" I've done with resin and coloring have been fun, that is some tough stuff!
One thing I like is the cost is very low compared to the epoxy I started out with. Basically the same stuff!
I agree with the temperature comment, certainly doesn't cure quickly, but the extra "play time" usually comes in handy.
Projects like these trays would open a whole nutter dimension, really just like the river tables on a smaller scale.