-> Use between 30 - 50 images per class (these numbers are highly dependent on which classes you are trying to classify).
-> Make sure the examples of images you used for trainning cover well the domain of images you will want to classify in the future.
-> Always test with different images than the ones for training to make sure it works for new images.
-> The first obvious limitation is the number of classes you can classify using this tool (right now only 2).
-> The number of images you can use to train are limited because it is being trained on the browser.
This limitations can be overcome with a custom approach but unfortunately not with this tool.