we have decided to try using MERGE MyISam tables on MySQL, to be sure we
are not going in crash with this decission we need some consulting.

we need answer for the following questions:
1. How safe/stable are they?
2. what is the max size for MERGE tables?
3. what is the disk size of MERGE tables (in addidtion to the traditional tables)?
4. any known problems/issues/bugs?

we need it from someone with field experience on MERGE tables (and not
from the web, we already did that).