There will never be a release of any complex software that does not contain any bugs, so if you are somehow thinking that X2b or X2z is going to be error free, you will be waiting forever.
While I do not have any statistics on it, I would venture to say that there are a large number of people out there using X2a quite successfully - even though there are bugs present.
If you are thinking of picking up X2 once another patch release comes out, you might as well consider upgrading to the current X2 - which then gives you access to the X2a updates. An X2b update would also be free, so there is no financial reason to hold off - other than perhaps not having funds available for upgrading now.
Bob Bone