On my 07 I ran stage one for about a year (no problems), stage 2 for about a year (no problems) and then was tuned for my 20G turbo and ran the car about 8 months (with a trip from Washington state to Maryland, back to Kansas) before deploying and without one single issue. This was all done with a Cobb AP.
I just happened to get the Cobb becuase it seemed better at the time. But I havent heard many bad things about OS at all either. It does seem to be cheaper, and just about as easy to use as Cobbs AP after you read up on it and all.
I have used both and both work well. I had an XPT stage 1 my 2007 wrx for about a year with no issues. I had XPT stage 1 on my 2009 STi for about 8 months through the winter with no issues also. I am currently using the Cobb Stage 2 map which feels really good also. The Accessport is definitely easier to use if you just want to flash a map quick. There is just no way a laptop and opensource software is ever going to be as easy as a tool that is made for the specific purpose of flashing the ECU. That said, I do feel like I have more control with opensource. I was able to disable air pump CELs easily which helped me pass inspection on my old car.
Overall if you are good with computers and want to learn then open source software and a tactrix cable will do everything you need it to. If you buy one and it turns out you think it is too difficult or not worth the time you can always resell the cable for like 80-90% of what you paid. Same thing goes for the AccessPort really. You'll never get your money back for the XPT maps you bought though.