I don't know which Delta we're talking about, but my experience with Delta's Key 6 Practice Tests is quite peaceful. The questions in the book are pretty straight-forward. I always get around 26-27 in both R and L. It's pretty high for me because I got lower than that in other books. Don't know if it's because I have improved or the book is too easy.
I'm also doing the 24 TPOs that have the same format like when you take the real test. I'll be taking the test at the end of Oct, so the clock is ticking right now. Wish me luck