I just got done using a Simon to install a Stage 2. I had the Stage 1 for a few weeks before getting stage 2.
The instructions are sufficient. But some of the menu options on the Simon aren't very intuitive. If I had to guess, I'd say the tool was designed in Europe. Maybe Germany based on my experience with SAP. Once connected, you have to select "Work" and then select the option to read the ECM. It's all spelled out, but you need to read the instructions first. You can't just do this on the fly.
Also agree with the OP on getting a battery charger set up before starting. I tried downloading the ECM file without it and it took about 45 minutes. Upload takes about the same amount of time.
After the Stage 1 upload I noticed a difference, but it wasn't as dramatic as I thought it might be. It took a good week or so for the car to adjust. After that it was great.
I took the Stage 2 for a 15 mile drive and I think it'll be the same here. Power is still good for just having installed it. There's seems to be a definite increase starting above 4,000 rpm. I need to put some miles on the car first to get the full effect.