I have the standalone QS4 USB Bazzaz on my gen 4 and knock on wood have had zero issues. Installed plug and play out of the box with factory settings. Not counting suspension or braking, this has been my favourite fun upgrade.
I have the new version of annitori. Its awesome and they have the best/fastest customer service in the industry. I couldnt even get someone on the phone at bazazz, i heard product is good but im not a fan of their customer service.
I have a Dyno jet quick shifter on my 2004. I bought the bike with it installed and have been wrestling with it since I got it. It works when it wants and doesn't more often than not. I've taken it off, reinstalled the map and the qs, it will work for a week and then quit. I know that's a lot of variables and for all i know its been on there the past 12 years but figured i would weigh in.