I have the Tadpole and it's a nice piece. Unfortunately, I understand that none were used in combat , thus making it useless for WW1 battle scenes. I've heard that there are plans somewhere on the web for converting it to a Mk IV, but don't know the source.
a few years ago Corgi Toys featured some ww1 models, die cast. Their Mk I? II? looked like the Airfix kit, be it the Corgi had rollers under the belly as far as I can recall. I only wondered if these ready made models are cast off's, their quality or beauty I do not deny as I still like my Emhar Tadpole even with the wrong sponson...