This is my name (as you can probably tell by my username) so this is kinda my view. On one side I like it since I think that bird names are always really graceful and cool, and it's kinda androgynous which is cool since I'm nonbinary and this was my given name, but on the other hand I live in England now and have lived in Germany before and it kinda sucks that this name doesn't exist in any languages other than Dutch so most folks just pronounce it as the English Meryl.
I don't necessarily love Merel as its vibe is too androgynous for my liking, but like both this spelling and the Dutch pronunciation far more than the English Merle. The meaning is also lovely. I can see this name being used and working well in the Anglosphere as the middle name, especially if someone either has some Dutch ancestry/connections or as a way of honouring someone named something like Merle/Muriel/Marla/Mirella/Meril/Meriel etc. Though I agree with one of the other commenters that it could be a bit problematic as a first name because it would be pronounced as Merle.
I oddly prefer this for a boy, but it's lovely for a girl as well! I think in the UK, where I live, it would just be pronounced like "Merle", which is not as nice as Meh-rel, which is the proper pronunciation. I love Birdie and Robin (male), so Merel is perfect! Again, I like it for a boy, and as girls are being named James, I think it is okay. :)