1) Every teacher who teaches a certain technique is going to put down another. My suggestion is to go take a few SLS classes and other methods like Bel Canto and see which you prefer. It is all about preference when it comes to a technique.
2) If it hurts don't do it.
3) Breath support is important but the SLS method is just stating that you don't want to make a big commotion about it like trying to suck all the air in from the room. Again, breathing should feel natural but come from the lowest part of the lungs right up to the top of them. The DIAPHRAGM does not take in are. It is a muscle that drops down on the inhale and then when you exhale it rises up and slightly inwards.
4) If you look at a lot of the SLS training it does have very good points to it because it talks about the bridges of ones voice which are where most problems with range come from because one does not know how to get through these bridges (The Passagio)

All in all, I believe in getting as much knowledge about the voice as possible. Try out different techniques before you pick one that you like the best. Make sure you get a reputable teacher though and don't just do the lessons off of the CD if you do the SLS method. Try to avoid teachers that avoid answering questions with a direct answer. You want someone who will give you the answers and guide you properly.

O,h and one last thing, an amazing Opera singer who graduated from Juilliard with her masters went on to study with Seth Riggs and she found it absolutely fantastic and loves his method after she studied Bel Canto approach for years. She is also a teacher in NYC and is very reputable. Her name is Badiene Magaziner if you want to check her out to see what she ahs to say about his method.