Also a [name_m]Potter[/name_m] fan here. I do think of it as a name for an older woman rather than baby, but I actually think that surprise would make me like it more. There’s so many [name_m]Potter[/name_m] fans naming their kids [name_f]Lily[/name_f] and [name_f]Luna[/name_f] that a [name_f]Rosmerta[/name_f]/Rosemerta would mix things up!
I like it! If you can get your partner on board, I say go for it!
I love [name_f]Rosalind[/name_f] for other people. Unfortunately it would be a no-go. [name_f]My[/name_f] step-MIL’s name is [name_f]Linda[/name_f] and I’m pretty sure it would be taken as a major affront to my MIL were I to use a lind/Linda like name… nevermind that I LOOOVE my step-MIL and would love to honor her.
I like it either way, honestly. I think it makes the most sense somewhere between the two, honestly, but that doesn’t necessarily make it any clearer. A very long o doesn’t quite work, but if you shorten the syllable but retain the O shape/sound, that’s how I feel I say it.
I don’t care for [name_f]Rosalie[/name_f]. I do like [name_f]Rosanna[/name_f] and [name_f]Rosanna[/name_f] is actually one I’m interested in honoring with the name, but it just doesn’t hold a candle to [name_f]Rosamund[/name_f] or [name_f]Rosmerta[/name_f] imo.
What I find interesting is that in the past the ert/mert of names like [name_f]Myrtle[/name_f] or [name_u]Bert[/name_u] really bothered me, yet [name_f]Rosmerta[/name_f] never has. I no longer actively dislike those other names, but I definitely see why people don’t like the sounds. Is it really THAT bad though, or just not a great sound?
I don’t love [name_f]Rosmerta[/name_f] because to me it sounds a lot like [name_f]Roberta[/name_f]. I am not a fan of the mert sound. I do love that [name_f]Rose[/name_f] could be a nickname though.
I kinda like [name_f]Rosmerta[/name_f], it’s definitely interesting. I think I just prefer other [name_f]Rose[/name_f] names more and I’m not really a fan when they start with the ‘roz’ sound.
I think it may be unappealing if it’s said in an American accent. [name_u]Bert[/name_u] is the first thing that comes to mind if it is pronounced like [name_f]Rose[/name_f]-murt-uh. But if it’s said in a Spanish accent or what I imagine Russian and [name_u]French[/name_u] accents sound like then it sounds quite lovely. [name_f]Rose[/name_f]-merr-ta with a rolling r is beautiful.
Fair question.
I don’t care for the name for several reasons.
Some of my most favorite names start with [name_f]Ros[/name_f] - particularly [name_f]Rosamund[/name_f] and [name_f]Rosemary[/name_f], and I vastly prefer them.
I had not heard this name before, so when I did, it sounded less like a person’s name to me and more like a product one would buy (a [name_f]Rosmerta[/name_f] mattress or [name_f]Rosmerta[/name_f], a new pharmaceutical).
While I love the ros part, mert is not a pretty sound to me (even though I get a kick out of [name_f]Myrtis[/name_f] and [name_f]Myrtle[/name_f]).
And this is completely personal and irrelevant, but I know some people with a last name along these lines and they are not nice people.
But if I passionately loved this name, I’d push to name my daughter [name_f]Rosamund[/name_f] or [name_f]Rosemary[/name_f] or something like that and then nn her [name_f]Rosmerta[/name_f]. She might insist you stop calling that or she might change her name to it. It’s always a crap shoot with names, right? 
It reminds me of the following words
Osmosis
Stigmata
I don’t really dislike it but I think I just love some of your other girl names so this one kind of takes a back seat?
I really like it! I don’t mind the “ert” part at all – but then, the R isn’t really pronounced in my accent at all. I say “roz-MUUH-ta”, kind of thing.
I think it’s a pretty, strong and interesting “[name_f]Rose[/name_f]” name, although I’m with you on [name_f]Rosamund[/name_f] being my favourite 
The only things that put me off slightly are:
I too associate it very strongly with Harry [name_m]Potter[/name_m], in that I’ve never really encountered the name anywhere else (although I know the mythology behind it having researched at the time). With names like [name_f]Hermione[/name_f], [name_f]Luna[/name_f] and even [name_f]Minerva[/name_f], HP is not my only association, but [name_f]Rosmerta[/name_f] is so uncommon that it is, for me at least.
Ros/Rose names are pretty fashionable at the moment, and even though not all of them actually derive from “rose” (like [name_f]Rosmerta[/name_f]), the sound is still there. I just think that [name_f]Rosmerta[/name_f] doesn’t feel quite as special and distinctive as she should, based on popularity and familiarity, because there are so many names that sound somewhat like it.
But on balance, I think it’s a great name with a lovely strong sound, and I do really like it!
Love: The history, mythological figure, and obscurity of the name
Dislike (I don’t hate the name): The sound
Neutral: The look, nicknames
I like it, but it kind of reminds me of soap or hand sanitizer.
I also love [name_f]Rosmerta[/name_f]! The history and sound are great. Unfortunately, the “mert” sound might be unappealing to some people or they might find the name to be dated.
Its the second half of the name that sounds bad to me. Merta (merduh) sounds half way between [name_f]Bertha[/name_f] (as in big bertha) and murder. That -erd sound is also reminscent of old germanic names that we generally assocaite with hairy warted characters in old fair tales, like [name_f]Gertrude[/name_f], [name_f]Ermentrude[/name_f], etc.
I also agree with this, the sound just doesn’t appeal to me 
Well, I tend to like [name_f]Ros[/name_f] names. [name_f]Rosamund[/name_f] is one of my top five names and [name_f]Rosemary[/name_f] is within my top ten or so. I like [name_f]Rosalie[/name_f] and [name_f]Rosalind[/name_f] fine.
So it’s not the ros part I dislike, its the merta. I had a great aunt named [name_f]Myrtis[/name_f] which I thought was an interesting name but frankly not appealing. [name_u]Mert[/name_u].
I had never heard this name before quite recently on nameberry.
I have to say it reminds me of a drug like Ativan or Wellbutrin. Have you tried [name_f]Rosmerta[/name_f] for your depression? That kind of thing.
And oddly enough it reminds me of a mattress brand.
I absolutely positively LOVE [name_f]Rosmerta[/name_f] . It is one of my favourite names you have brought up and every time I see the name on here I fall more and more in love !
The Merta part sounds like one of my least favorite names- [name_f]Myrtle[/name_f].