I did a free trial with them over the summer, and overall I'd say not worth it (sorry, can't vote on the mobile site!)
There were some OK->good books, nothing really amazing and a lot of average->poor books. There's a lot that you could get free or very cheap on Kindle anyway.
I felt like I wasted time sifting through the poor ones, or downloading and reading a bit, then ditching them. Like you I decided I'd rather buy good ones by authors I know I like, supplemented with charity shops and library (when open) for mediocre/take a punt books
The best for me: the Vine Witch, Wakenhyrst, Dreamland, Death on the Nile (I think there's a couple of other Christie if you haven't read them)
Pretty good: Pachinko, Paper wife, Daggerspell
Harmless readable trash: the Lee Strauss Ginger Gold series, Everland Ever after series.
Obviously it depends on the sort of books you like!