The reason is because higher rank recipes stay orange longer, so you get guaranteed skill points longer. The rank 2 of this recipe turns yellow at 135, while the rank 3 is orange up to 145. The rank 3 also cost fewer materials, so you will save a lot of materials by getting the rank 3. You could actually level to 150 with the rank 2 recipe, but it will be green for the last 8 points, so you will have to spend a lot of extra materials, and there is no reason to rush 150, so I recommend to wait until you get the rank 3.
Since it's like a premium version and it's not modifying game files it gets by somehow. I personally hate Zygor's guides and always have, it's just personal honestly. I understand some people like his guides and have no problem paying for them but I personally hate the idea of charging someone for an addon that - as this post points out - has plenty of bugs in it. These were fixed last week and if I'm paying cash for an addon I want that addon bug free and not causing a hassle and taking my time away when I could be doing a better job without an addon at all.
For reference, my previous best time abusing Method-0 in 7.3.5 was 32.4 hours(as show in the old thread). A difference of just over 8 hours; which isn't all that bad, all things considered. And I believe I made several errors along the way, which could be cleaned up in future runs. I believe that that gap could be significantly closed by using a monk's bonus, but I hate playing monk...so...yeah. YMMV