The goal is to increase reading speed and comprehension levels and this can be easily accomplished by old fashion reading. If you dedicate just 30 minutes a day to reading while preparing for the DAT that's a lot of reading accomplished over the course of your preparation. Make it a habit to read just before bed, not on a computer or phone but an actual book or magazine, it will also help fall asleep. Old school still works for certain things. From experience trying to predict a score for reading using a timed test is not possible there are too many variables . We offer free daily reading passages in our study group that can help with practice, others can chime in about the other products you mentioned.
I agree with @orgoman22, you really just need to keep up with your reading. I read several science-based articles every day and asked myself after reading each one if I could summarize what I read. If I couldn't, I would reread it as a sort of punishment/training. Doing that alone helped me score as high as I did. Plus, it saves you money too, which is nice.
If you really want to have practice questions, try some RC GRE tests online for free or the Kaplan RC section. I heard both work well for those who want that resource.