Potentially an excellent tool, but contains serious mistakes
I have been using this app for a few days and it has made it far easier to memorize verb forms. The dictionary alone is a great tool to see everything relevant laid out for each verb.
Unfortunately, it contains serious mistakes. First, there are problems with the compounds of pôr (compôr, pospôr, etc.). These are conjugated as though they were regular -er verbs. As an example, for compôr, instead of eu componho, ele compõe, nós compomos, eles compõem, what appears is eu compo, ele compe, nós compemos, eles compem, and so on through all tenses and moods, for all compounds of pôr. As a result, virtually every form is incorrect. Luckily, these verbs are put in their own category, so you can ignore them until this is fixed.
Some future subjunctives are also incorrect. For estar, this app gives estivar, estivarmos and estivarem; it should be estiver, estivermos, estiverem. Similarly, for dar it gives dar, darmos, darem, instead of der, dermos, derem.
Finally, students of Brazilian Portuguese might want to note that they don't need the "tu" form, which is replaced by "você" in standard Brazilian Portuguese. Although it's good to see what these forms are, it would be very helpful if one could exclude the "tu" forms from the quiz so that one can work on just the relevant forms for Brazilian Portuguese.