To answer the 1st, the SOA is made by Full traction. I love it and haven't had the first trouble from it.
2nd, OH yea, my springs are flat. My Dad''s are worse, his are a little more flat than mine.
3rd I didn't have to extend the drive shaft. The only time I had to mess with the DS is when I did my AX15 conversion and that was WAY before I put the SOA on.
As for the extra stuff under the axle, I really don't notice. It's not really an eye sore or anything. I love my set up. The only thing I have yet to do is install the trac bar. As it sits the rear leafs hop when I take off from a stop.
I have thought about getting stronger springs but if I did then I would definately have to add a SYE first cause. As it is now the springs work perfectly it's not too high and doesn't bind the DS.