The SNS is a plastic bottle that has two tubes coming out of it. The bottle hangs upside down from a string around your neck and basically works on gravity. There are three different sizes of tubing for different thicknesses of formula or for baby's special needs. The Lact-Aid looks more like an iv bag, has one tube and works by baby sucking...not by gravity (it doesn't hang upside down, you just clip the neck strap onto either side of the bag). I've found that the Lact-Aid produces better results...baby has to suck "deeper" to get the milk. The Lact-Aid also works on the bag system, like a Playtex disposable bottle...baby gets a clean bag every feeding, no need to sterilize the container. The SNS has to be cleaned after every feeding. With the Lact-Aid, you can prepare several bags at one time and just put the top on and go. If you go for the Lact-Aid, you need to have several "units"...that's the part that has the tubing. The SNS is probably more cost effective, but in my opinion, the Lact-Aid is best!
Hope this helps!