I personally used medify for ucat prep then medentry for interview prep. I would say they were both pretty good and adequately prepared me for the UCAT and interviews respectively. That said, I believe that some of the medify UCAT questions (most notably the AR and QR questions in later mock tests) don't accurately reflect the actual difficult of the ucat subsections, being much more difficult than the actual thing. Thus, I know a lot of people who used both medify and medentry in conjunction (from what I've heard, Medentry also has some problems such as very wacky scaling for mock exams).
