I agree. Try the DVDs. I have all the Signature Series DVDs and love them. I found the upper body DVD to be the most difficult. Even after a two-month rotation I still could not complete the plank section without breaks. It will definitely increase your upper body strength. And has an added bonus of improving your posture. Everyone commented on how it looked like I had gotten taller when I did this rotation.
You can just start out with her Total Body DVD, to see if you like her style. I found it difficult but doable. I haven't done it consistently enough to comment on strength gains, but I do feel like it would work towards that if done regularly.
I can't comment on the periodization system because I haven't tried it. Although, I do plan to get it eventually because I really click with her style. I just want to be able to complete the DVDs without breaks or modifications first.
Hope that helps.
Jen