Does the merge system support the latest version of phpbb? I'm running 3.1.6 and was thinking of converting to mybb as its a lot simpler to use.
As far as I'm aware, it should work fine. MyBB doesn't modify the phpBB data at all, so there's not really a risk to attempting it. If you have any troubles, let us know and we can help you out!
There may be a few parser issues (especially with smileys) and forum moderators are likely merged wrong but apart from that I'm not aware of any issues with the phpbb module. Feel free to report any issues you notice.