I’ve actually taken both the DAT and the OAT (I made a switch to being pre-optometry), and I had separately used the DAT Bootcamp for the DAT and Chad’s videos for the OAT. In my opinion, DAT Bootcamp provides the best and most realistic practice for problems you’re likely to encounter on the actual exam. I would definitely use Chad’s videos for physics though since Bootcamp doesn’t provide informational videos on it. As for how long to study, it really depends on how much time you’re able to commit each week. For most people, at least 3 months is a pretty good time.
tldr; Bootcamp is great for the OAT, but also use Chad’s videos for physics. Give yourself at least 3 months to study