Not bad but...
A) I actually use this App since many years and despite its good idea behind the training of words towards memorization it is in fact extremely hard to memorize individual words without a context or phrase. I do recommend its use but not as only App ..actually it would be great if someone develops a “common phrase audio/visual trainer” B) The splitting of the HSK words in small groups of 15 to 50 words each is a pain in the ass as each group has to be downloaded independently; that is specially painful if you change or upgrade your phone, you have to painfully download each group manually one after another...they should have an option to download multiple groups or a complete ser eg HSK5 at once. C) Once ugly feature is that the size of the 汉字 is as small as the pinyin and the pinyin is even highlighted ...the App makes bad use of space and should draw 汉字at least twice as large. D) The App doesn’t support phone /tablet rotation so when I project my phone screen on the TV the TV screen usage is only 25 to 33%...bad, because what I wanted is to enlarge the Chinese characters....E) This one is really bad, the group of Business Chinese characters (about 600) are totally random and not aligned at all with the official BCT-A (~1000) and BCT-B (~1400) set of characters. F) Another terrible feature is the “Practice all” which starts on the very first group downloaded , so the starting and ending training groups cannot be chosen at all and if the App remains idle some minutes there is no memory of what was the last trained word/group. Then the only option is to manually select the group to train ...imagine that you want to periodically practice different groups HSK3,4,5, BCT..you need to painfully select one out of literary hundred of individual groups and there is no memory nor indication at all of which one was the last group you trained. I hope the App will be improved to solve all those ugly features or lack of them. Thank you, JC