The Iridium GO! exec and Iridium 9575 have an SOS button for an emergency response service at no additional charge. The Iridium 9555 does not have an SOS button.
The GO! exec has 50% more battery life than an Iridium phone, with 6 hours of talk time compared to 4 hours on the Iridium 9575 / Iridium 9555
The GO! exec has a built-in speaker like you would expect on an Iridium Phone and the same voice quality.