The legality depends on what state or country you live in. Most states that ban switchblades include language in the laws about a button, lever, or other mechanism that releases the blade (which may be spring loaded or open through gravity or inertia). Assisted knives however usually circumvent those descriptions because the blade itself is being moved.
What state do you live in?
Frankly, an auto for about $50 really isn't worth owning except as a novelty (and even that's arguable). And personally, I'd stay away from SOG. Their mechanisms are unnecessarily complicated and a serious PITA if you ever have to disassemble them for cleaning/lubing. Go with Kershaw. You can get a D2 composite Leek for $60, or any number of other ones like the Blur for the same or less.
Even though you said not to, I do have to mention Benchmade, because if you're interested in autos or assisteds, it's obvious you're interested in speed. And a non-assisted, non-auto Benchmade AXIS lock is the quickest, and easiest knife to both open and close. You can easily flick them open, either using the stud/hole, a strong flick of the wrist, or you can pull back on the lock and very easily wrist flick it open. More importantly, you can flick it closed just as quickly. You can't do that with an auto or an assisted. The only thing that comes close is a D/A OTF auto, and one worth buying will cost you $200+. Or a fixed blade. A Griptilian or 530, while more than the $55-60 a SOG Trident or Blur will cost, is still under $100, and IMO well worth the extra cash. Better lock, better steel.