Update:
App has changed to subscription model, so not all below applies...
I was hesitant to buy EllaVerbs without trying it, but am so glad I did! It is easy to use and flexible, no nonsense but still feels fun. The way it divides learning verbs into categories like, stem-changing e to ie verbs or irregulars makes learning the verbs so much easier. I’ve heard this approach recommended by teachers (like the Spanish Dude) and have found it very helpful. Also the explanations of how to conjugate are concise but informative. EllaVerbs feels like it was written by a good teacher / Spanish enthusiast not just a developer trying to make a buck. Also I like the fact that you don’t have to go through a huge instructional phase before quizzing, you can dive right in or choose to read the tutorials.
One piece of info I couldn’t find before buying was what verb forms it includes. As of this review it has: Present, preterite, imperfect, past perfect, future, future perfect, conditional, conditional perfect, subjunctive, subjunctive imperative, subjunctive present perfect, subjunctive past perfect, and imperative. Each section divides up into regulars and irregulars, with irregulars divided up into logical sections as mentioned. There are also options for taking quizzes mixing verb forms as well as a quiz on the ones you’ve missed.
Very well thought out. Highly recommend.