This isn't a third octave altissimo key that lets you play in-tune altissimo without using altissimo fingerings. It's only there to help make high G play better, like a high G key on some soprano saxes.
Yeah, that doesn't work so well on alto, but for alto, you should give improved G, side Bb and ***/1** a try, and if you want a big bright G, try 1*3/1*3. No octave key on either of these.