I find the (random?) selection of sentences to play in Hands-Free Mode rather erratic, with some sentences being played too often and some played very seldom or hardly ever.
Some sentences being played too often can be experienced even in very large collections, where the sheer number of sentences would preclude any sentence to be played more than once during a short session, with some sentences still being played more often than others.
Some sentences not being played at all, or very seldom, is easiest experienced in a small collection (say, 30 sentences).
I have not found any pattern with regard to the sentences that are favored and disfavored, so my guess is that it has something to do with the implementation of the random selection.
This problem didn’t bother me so much until I started using the Hands-Free Mode on my Favorites; I find that by using this mode on my Favorites every day I learn a lot better than by staring at the screen. But, at the end of the day, when I play the Favorites in an ordinary session, I find that some haven’t been played at all in the Hands-Free session.