Hi all,
Just for comparison.
The biggest weakness of San He ZWDS, IMHO, is : Tai Ji concept.
In other technique of ZWDS, Tai Shui Ru Gua, used Tai Ji to attach other people DOB to your destiny reading. That's way, people with the same DOB, have a different luck. People around us, give a different impact to our life, depend on it is suitable or not. In ZWDS you can analyze that thing.
Si Hua is logical, but there is a doubful of the technique to fly Si Hua. San He in other hand, use a different technique for annual chart.
But both have a same technique for flying decade Si Hua. Si Hua school still use the same technique like decade, but San He use stem of current year.
Which one is fake ? 
Till now, both school claim, their method is very accurate. 
Just my 2 cents.
Best regards,
X
Hi X! Its good you post this questions. I tried to answer your post but it didn't get through and what I typed are all lost.... So here I go again!
We talk about tai ji.
From tao comes tai ji. Yin and Yang. From Yin Yang comes trigram and yi jing.
ZWDS enbraces tai ji.
San Fan Si Zhen is space. LP is time. I call it cosmos in your palm.
What is Dou Shu?
Dou is star. Star characteristic. astronomy.
Shu is calculation. numerology.
I bring across an idea I have.
Dou is star, is yang, is 'sanhe',
Shu is calculation, is yin is '4 hua'.
This is the yin yang, the whole of Ziwei.
But even with half you the equation, each school are accurate enough in the readings. To me Ziwei no sanhe or 4hua. Both are tools which you can use the Dou Shu more accurate.
So sometimes there is no point to compare Ziwei or Bazi or other metaphyics. Its whether the person is accurate or not.
A doubtful of Si Hua is, it ignore Stem of current year. So what is the function of the current year Stem ?
Si Hua only use Stem from palace. 
Si Hua school still use the same technique like decade, but San He use stem of current year.
We do use the stem for yearly. Eh... Why Si hua school dont use yearly HS?
Ask me in another post if i forget to answer you.
Si Hua, emphasize is Tai Ji. How is one palace interact to other palace. Si Hua school still use the stars.
Ziwei Dou Shu IS about how one palace interact with one another. Sanhe or 4hua, its the same! Haha....
Without the stars, we really can change the name of this system.

Really! ZWDS is a very unique system, most of the past systems (including Bazi), uses the '5 stars(as in the 5 elemental stars) in their reading. And it is the only system I know that don't uses the HS, EB of month, day and time.
Just my 2 cents,
Have a fruitful journey into ZWDS, my friend.
Cheers!
L