JMS,
I was decided to change the standard rear suspension due to the harsh feel and lack of dampening, so I started looking. Since my problem was not handling related, only comfort and softer ride in general I looked at the air suspension for the first time in my life. Read a lot about what other riders had done and I felt there was a general consensus about how much better they felt with regards to softentening the ride while going over bumps. That I have now tried and I can join the happy "air riders team". So hopefully no more back Ouch! feelings.
I was also looking for a change that would lift my bike as much as possible since one of the other problems the Springers have is the lack of road clearance; I hate scraping my footrests, side stand ASO. With this pneumatic suspension my bike at máximum lift is about 1 1/2" higher if not more and I´m pretty sure that difference will definitely improve clearance with the road. I haven't tried that much yet, but I'm very optimistic about it.
Oh, and I almost forgot the one thing that made me clearly decide to go for the SAS; that is the lack of tubing and complicated installation of the whole system, where you have to find a place for the compressor and so on.
Not very pleased with the lack of info or the poor quality of the electrical wires and no hardware to install it, having to buy spade connectors, fuse holders, switches etc. It costs peanuts to them, and it creates a big problem to the purchaser; I just hope they change that policy because the product (meaning the suspension) is a great piece of engineering and manufacture.
Hope I cleared your questions

BR,
Spanish Flyer