Probably better to gain traction on one platform first. If it is working out well you have found the recipe and it's likely to work on other plattforms as well. By adding other platforms you will multiply the userbase by 3 in the best case. Increasing the installed base on one plattform in an early stage will be more effective.
In many cases I'd say you are right, but the scope of this application looks limited enough to be able to port the application part over to Android really fast, especially if the author already has experience developing for Android.
Most of the work for this product is probably in the backend, which I assume does not need to be changed to service Android clients.
