I think it's a great idea that someone has put a low-cost autopilot system for helicopters on the market. I think it is a great pilot aid for VFR flight.
But ironically, the one thing this system is NOT is a "SAS." The name choice is most unfortunate because it is misleading.
The reason the Chelton/Hoh system is low cost is because it uses "parallel" actuation only. That means it works in parallel on the controls, applying force through a spring. It's like having someone in the other seat on the controls applying force to correct your flying. But other than the sensation of spring force back to the pilot, there is no real assistance to stability when the pilot is on the controls.
A true Stability Augmentation System (SAS) or in some cases a Stability and Control Augmentation System (SCAS) works in "series" with the controls and adds or subtracts from the pilot's control inputs in order to augment the stability or boost the control input as the flight situation demands. For example, in turbulence a governed power system will increase and decrease power which in some helicopters leads to tail wag. A true SAS or SCAS system will detect the power changes, see the wag, and put in the corrective yaw control before the pilot even notices. And all this happens without the pedal positions ever moving. A true SAS or SCAS does this same thing on pitch, roll and yaw and actually improves the flying behavior of the helicopter. It can fix handling quality problems like the power/attitude to airspeed/altitude relationship. This is especially important when you are trying to meet the stability requirements specified in Appendix B of the FAR 27 and 29 for IFR.
So a helicopter autopilot with "true" SAS will have fast-moving series actuators to improve handling and stability, and slower-moving parallel actuators to control the helicopter when the pilot is off the controls. The SFIM autopilot mentioned (which became SAGEM and now SAFRAN) has a basic 2-axis autopilot (pitch and roll parallel trim actuators) with a 3-axis SAS (pitch, roll, and yaw series actuators) So this system provides a true SAS. To that you can add a yaw damper computer with another parallel actuator on the pedals. To that you add a flight director computer for coupled ILS and the like. (In true SAGEM fashion, the intent seems to be to sell as many boxes as possible.) This causes it to be a somewhat overpriced system with a more-complex-than-necessary installation.
But it is a more capable system.
IFR Helicopter autopilots like those in the S-76 and 412EP usually require 2 sets of series actuators on each axis driven by independent computers. (That means the system has 6 series and 3 parallel actuators) . Each of the flight control computer uses a separate set of flight sensors. This is because the series actuators operate rapidly enough so that if something went wrong, they could turn the helicopter "dirty-side up" before the pilot could notice it and grab back the controls.
So you need a second system, just as powerful as the first that will immediately add or subtract control input in the opposite direction to keep the helicopter "dirty-side down." This is called "fail passive" operation.
4-axis autopilots add a 4th trim actuator on the collective. 4-axis autopilot allow you to couple both a speed and a vertical mode (like glideslope) at the same time. This is really nice for the new WAAS steep helicopter approaches where you want to have the glidelope on collective and speed on pitch.
But back to the "HeliSAS" system: It is a 2-axis (pitch and roll) parallel-actuator only autopilot system. (2 faster moving actuators than traditional trims as I understand it). It can fly the cyclic when you need it, and nudge in corrections to your hand flying when you are on the controls. In a lot of cases, that's good enough and it's a handy aid to have. Unfortunately all these systems are called "Autopilots" and the word SAS in the name doesn't mean you are getting one. Be sure you know what you need and what you're getting.