I needed to make another database synchronize with the OSE membership.
He answered my technical questions with additional hints for everytime I asked.
I owe him much gratitude.
Compared to another paid membership extension which I once introduced to my site,
this extension is easier to introduce and its bug fix is held more rapidly.
Though I'm satisfied with the quality and the support of this extension now,
if I try hard to find a drawback about this extension for you,
it would be the lack of the information about how to develop a cusom addon.
I'm afraid it may be only for my case,
but he and the wiki documentation about it's API tells me to write my code directly into the source,
which will require me to maintain my code when the source will be updated by the developer.
This extension would be better if it was, and if so, I might not bother him again and again.
If you have a pre-sales question, the support will answer soon,
and you'll be also satisfied with his answer.