After recovering from the Beta 3 Setup bug my installation of Beta 4 went smoothly.
The bug fixes have improved usability of Passage Lists from a Search, improved the generation of searches from Context Menu and BWS, fixed bugs in the Collection & Search panels and elsewhere, but most importantly Merge is back.
There was a bug with merge in the Bible index but that has been fixed and the merges I performed on the main Library index have been successful and fast (8 minutes vs 52 minutes for a Rebuild). What has your experience been?