LatTinSFThank you Mirna for your kind words!!! I am happy that my story has helped you to keep going!
The Manhattan guides were essential for me as I studied "0" for the GMAT between October, 2011 and May, 2015. My knowledge was a bit rusty, but these guides helped me to build a foundation for my GMAT prep. When I started preparing for the GMAT again this year, I was probably at the low or mid 600s. The old 3-month
Magoosh plan was perfect for me because it included the Manhattan guides. So if you are at about that level, I would recommend that you use that plan instead of the newer one. I felt that the old plan included more concepts and less practice than the new one. The old plan also took probably about 50% less time per day for me than the new one. If you lack the concepts (or just studied them a while ago and a bit unsure about them) and do not have much time to study, use the old plan.
The new 3-month plan assumes that you already know and comfortable applying what is included in the Manhattan guides. In my opinion, you already have to be scoring in the high 600s to get the most out of this plan. This plan does not include the Manhattan guides. I only reviewed the guides during the last week of my GMAT prep because I already went through them during my first 3 months of study. This new plan has hard core LSAT practices for CR and RC, and it also includes the Manhattan Advanced Quant book, which is a great resource to get a high Quant score. That is the reason why I included it even in my old 3-month
Magoosh plan.
You have to figure out where you stand. Take a GMATprep practice test. If you get a score close to 700 and you did not guess on many questions, go with the new plan. You can still use the Manhattan guides by following how the old plan includes them (how they are divided among the days), and go through them at the beginning of the new 3-month plan or even before you start the new 3-month plan (max two weeks should be enough if you do not do any other GMAT prep). Also, review them during the last week of the plan to refresh the concepts before the exam.
If your recent practice score is closer to 600 than 700, go with the old plan. In this case, the guides are already included in the plan.

If you make a mistake on the actual GMAT and you do not get the score you want (as I did...), you will have a chance to improve by going through the new plan. If you start with the new plan, you won't have that chance because the old plan prepares you for a lower level. Of course, it is the worst case scenario.

I hope my answer helps!
If you have any more question, please let me know!
Best,
Andras