I've been using their FSX Booster V2 prog for a while, I find it improves overall performance on my system, however a) you need to play around with the setup and b) when it gets updated - which is regularly - you have to uninstall the current version and down load the updated one and re-install. At around 16MB a time, I usually wait a month or so before updating. That aside, I think it is a good addon. My system is mid-range, however it still stutters at times.
I also bought their Multicore environment utility a while ago. This was a waste of time IMHO, and has not been re-installed the last time I had to re-install FSX after a system crash. The different PC setups react differently so what I say works well on mine may not be the case on someone else's.
