A couple of gripes/suggestions:
1) I've had situations where, for example, in the extreme righthand column, after making a vertical word, the top three letters are, in order, a "hot J", a "broken Q", and a "hot R". In this case, that last column is taken out of play completely through no fault of the player. No words end in "J" or "Q" (that are accepted) and no words begin with "Qr". Suggest you modify the model to not allow this to happen.
2) On more occasions than I care to mention after making a word, I'll see a 2X, 3X, or 4X gold tile appear for a split second, only to be gobbled up in a low scoring wordimmediately by the cascading letters, either vertically or horizontally. If it were to happen because I left the other three or more letters in place that create the word, I could accept it. But when it happens with JUST the letters that your model is delivering, either after a vertical or horizontal word, then it's very frustrating. So, as an example, if I made a seven letter vertical word like "samples", and the system replaces those letters with "lustqzx", where the "L" is a 4X gold tile, it automatically creates a very low word score with "lust" and wastes a gold tile for future use.The player works hard to save the gold tiles, particularly 4X tiles, and they come along rather infrequently. It seems like an unnecessary frustration to the player. Suggestion, never deliver a gold tile with a group of letters that will automatically make a word all by themselves.