The merge is too complicated and to inflexible. PLEASE compare with WordPerfect. I have been using LO merge for a client, having *finally* produced a 32 step procedure to remind myself how to do the same thing once a month ... because the nonprofit client can't afford WordPerfect and HATES Word. But for new projects, Libre Office's merge-print is much too complicated for me to use ... and I am a veteran merge-printer with decades of practice.
For starters, users might want to set up their own fields, but LO's fields are fixed. For an efficient mail-merge it is often useful to combine full names -- not everyone's name falls into the neat First Name Last Name format; my wife and I have different last names. A Fullname field is much better. Why can't variables have their own names, as in WordPerfect?
Next, connecting a spreadsheet full of data is fraught with problems in LO, but transparent in WP. That, too should be easier ... even easier than WP, that requires a coding step to get the fields identified. Why not require the first row to be the headings (as in the LO Calc sort) and go from there?
There is then considerable unintuitive clunkiness to the LO merge process: files that appear to be saved but aren't. For a first timer, the learning curve is a wall.
I would happily interact with the Merge team, and work on beta-testing a simplified wizard -- that's surely the way to go.
Could you please give a try to a recent LO version? 5.2.4 is last stable one.
You can also test prerelease 5.3.0 (see https://www.libreoffice.org/download/pre-releases/).
It's very useful to have a feedback from an experienced user, but if there's no response to a message and this stays open for 6 months, then this one cannot go on.
Since LO 5.2 merge wizard is different, 5 steps instead of 8. But wizard is not the only way, merge can be used directly, not clear from here. There are a number of bugs filed as linked to Bug 102998. Those may be different, though.
Bugs are reported separately and need to be understandable to non-user so steps are used: what is reproduced, what exactly is expected.
An example: You say Fullname field is much better than First Name Last Name. But what if you want "Mr. X"? Why can't you simple put "First Nick" as First and "Last1 Last2" as Last or whatever? That' a discussion on it's own.
"connecting a spreadsheet full of data is fraught with problems in LO"
Needs to be explained in steps and details to be reproducible.
"files that appear to be saved but aren't. "
Similar, not clear.
"set up their own fields" Needs user case and explanation. May be relevant, although I don't need it myself, you can match whatever you want.
I can only close it now. You are welcome to add new info and set back to Unconfirmed.