Different Dave here
Last year I bought one used from someone in this forum and it immediately paid for itself! I had already wasted the money on the little Bluetooth OBDII adapter to connect a mobile device so I could passively read codes. I also wasted money on two increasingly capable code reading and diagnostic tools, like iCarsoft. But when push came to shove, they still couldn't do everything I wanted. Like something as simple as telling the car it no longer has a CD changer. Or like telling the car to no longer automatically raise the rear headrests anytime the rear seatbelts are buckled. (Kind of pointless when 99% of the time it's my little ones who are way too short to benefit from the head resets anyway)
Just a few days ago, on my '06 S500, I thought my gear selector had broken and stopped working, and assumed it was the dreaded broken plastic lockout lever. After playing with it a bit I couldn't start the car anymore nor get the key out. WTF?
But before pulling anything too far apart, I decided to "be smart" and see what SDS had to say about it.
After going through the hassle of pulling out that old laptop, MUX box, and cables, getting it booted all the way up, connecting the cables, going into the Star Diagnostic System, and finally drilling down to the transmission area...18 minutes later... It said the gear selector was in one gear, but the transmission itself was in another. Huh? That didn't make any sense! Especially since I "just" backed the car up a few feet, pulled forward again, put it in park, and turned the engine off.
Within SDS moving the gear selector DID register as moving between P, R, N, & D, but the transmission still remained in the same gear. Which totally changed my guestimate of what the problem was.
So then I looked at the shift rod linkage underneath the car. It had simply fallen off - because the rubber bushing was completely gone!
I stuck the rod back onto the selector box link and voila - things worked again! I couldn't pull the key out because the rod had fallen off right before it got into park.
That's the kind of reason why you want an SDS system.
The next day I picked up two shift rod linkage bushings for $6.50 and popped them into the rod ends. Not only did that solve my primary issue, but also the occasional issue of the dash displaying the message "Move selector into park" after I had already done so, shut off the engine, and was exiting the vehicle.
Without the SDS I would have assumed it was the plastic lockout lever and gone ahead with ordering that part and just left the car as undrivable for the few days. Instead I was back up a running a few minutes after using it.
A few more examples (for anyone interested in more reading):
When I had the rear interior pulled out for a couple of weeks, I also had the third brake light removed. Every time I pressed the brake pedal one of the rear seatbelt retractors would click very loudly. It turns out the computer just needed to be told the third brake light was no longer installed. Problem solved.
There is a leak in the front seat bolsters that I've yet to fix, and won't until I completely redo the leather in front. I was able to use SDS to turn off that system so it no longer runs the PSE pump every time I turn on the ignition. Thus saving my PSE pump from unnecessary wear!
When I change my oil and air filters, I use SDS to tell the vehicle the service has been done, which resets the counter within the dash.
My tire pressure monitoring system (TPMS) began misbehaving. I get sick and tired of having to push the damned button on the dash everytime the car wants to nag me about it. I used SDS to "remove" that system from the car, until I got around to fixing it. Then I used SDS to turn the feature back on.
I've only had the SDS for a year, but I can go on and on about how much you'll wish you'd bought it sooner!
Okay...whew... I'm done with my pontificating for the day.
Hope that helps!