I've seen a few threads about these things, more specifically if the HVAC memory is saved when using one. Well, today I got to put one to the test in an Envoy.
The HVAC, radio, drivers seat memory, and obd2 readiness (among other things) were retained after the battery was unhooked for close to 45 minutes.
After the repair, I didn't get much time with the Envoy to see if the idle had been effected. This is another thing that I'd like to have an answer to, so if I get another in the shop and can verify it, I'll follow up in this thread.
The unit used was the e-z red MS4000.
Also, the crappy pic is supposed to show it plugged into the obd2 port.