Toy vs Bowl - Work for your food or have it for free?

If given free choice of a food toy or a food bowl, will the dog choose to work for their food or have it for free?
This is the outcome of several days of testing this out with my two border terriers. The toy and bowl had roughly equal amounts of the same kibble. They had previous experience with all of the food toys shown and are often fed their meals using these. We varied which item was closest to the dog and which was put on the ground last. Dog had completely free choice which to take first. They were left to finish their food at their own leisure (and in all cases ate all of everything!).
The results surprised me!