I've been a little out of the DSM thing for a couple years but I've got a SAFC and a DSMLink, the big difference is that the SAFC installs between the MAS and the ECU and can only intercept and alter one variable, which is the MAS output. I'm simplifying somewhat, but the way I understand it is you put in injectors that are 12% bigger than stock, and then the stock ECU doesn't know that and ends up injecting 12% too much fuel all the time. So you use the SAFC to reduce the air input by 12%, so that throws off the A/F calculation in the ECu by 12% and it injects 12% less fuel than before, which errors end up canceling each other out and you get the right A/F ratio. Now the benefit is that you can get 12% more air in before your injectors get to full capacity, right? This is all fine and good except when you start to alter things too much. Say you put in 750s, that's 40% bigger than stock. You can adjust your SAFC to 40%, sure, but what happens inside the ECU is now you're on it pretty hard and flowing tons of air and the ECU, because it's seeing airflow numbers 40% lower than reality thinks you're only under moderate load so it switches ignition maps to a more aggressive low load map and you start knocking because you're on the wrong timing maps and the SAFC can't do anything about the timing.
So functionally I think the SAFCs work quite well with 550s, somewhat decently with 650s and poorly with any bigger injectors. The benefit of the DSMLink is it sees everything the stock ECU sees and can see real numbers because it's inside the ECU and can get rid of the obstacles we were trying to overcome with lying thru the SAFC, namely fuel cut. Also, you get fringe benefits like rev limit control, different outputs for the stock boost gauge (knock, timing, etc), and fine tuning control over the timing and fuel maps with a base injector size alteration so the ECU can make A/F calculations using the proper injector flow rate. Also the ability to log boost, fuel pressure and wideband 02 is pretty cool rather than having to watch the road and those gauges and then remember all the outputs when viewing logs. Don't forget the support network you buy into with the Link forums populated with other users and the guys who made the thing in the first place.
To set up a safe but fun daily driver with evo3 16g, 2G MAS, 550s, and the usual FP, exhaust, maybe intercooler, etc a SAFC would be a great choice but in my opinion if you were going to go farther than that a DSMLink or comparable alternative would be a far better choice.
