That is why I have been adamant about only using stock MII X-members and hardware in my installations and advising everyone who asks to do the same. These aftermarket guys are probably not engineers and I am 100% sure they don't do fatigue testing to check the long life implications of their designs. I recall one guy posting on a thread similar to this last year that he tested a new suspension he was planning on selling "all weekend, over potholes and rail road tracks" and didn't have any failures so he was confident in selling it to the public.
I know for a fact that Heidt's 'economy' X-member has a serious flaw in design that will invariably fail with enough fatigue cycles. There have been a couple of pictures of the failure posted on this board in the recent past. I am not familiar with Fat Man's design but it sounds from your description that it has some serious long-life design flaws too.
If you have one of these after market X-member, be very diligent in doing your monthly inspection looking for cracks, bends, and evidently, failing bolts.