Hi Ellabella,
It’s a tricky call...
we often talk about vintage buttonholers for their quality buttonholes and ease of use.
There are 2 factors in this.
1) older vintage machines (pre 1940 were straight stitch only and produced excellent stitches- the singers 66, 15, 99 and famously the 201 (but were still sold into the 60s I think). The quality of the stitching and the ability of the machines to penetrate effectively most house hold fabrics was important. Fabrics were heavier due to there being less heating, so they coped a lot better than modern machines with something gnarly, and don’t fuss much.
2) because they produced only a straight stitch the button holing attachment was invented... these move the fabric to allow a straight stitch to zigzag. There are generally 2 formats 1) with a length and bight settings and 2) which is cam driven, you adjust the bight and insert a cam and it makes a buttonhole in the style of the cam. (My favourite because I love keyhole buttonholes.)
The buttonhole attachments produce easy reliable buttonholes that once they’re set/have their cam just require aligning and sewing, and it’s job done.
However part of this is the exceptional stitch quality/penetration of a straight stitch only machine this means that whatever you are sewing, gauze silk, tweed, canvas, (possibly a tin can in the case of the 15k) the number of stitches skipped and amount of fuss over multiple layers of fabrics will be less. So the buttonholes are more reliably successful.
Having said that a manual buttonhole on my 500a/401g is still a nice buttonhole it just requires 4 stages and a close eye on the instruction manual... so I bought a pink atomic cam driven buttonholer for it (definitely nothing to do with the mad styling). When these were available zigzagging was well established in sewing machines and they’re designed for 401s/500s/600s but the simplicity still made them popular devices despite being technically redundant at this stage.
Having said that if a buttonhole attachment will fit on your modern machine I still reckon it’ll produce an easier more reliable buttonhole. But I haven’t tested it, because I love mechanical machines and don’t really go later than the 60s...
I work with computers and clouds all day and don’t want to do hobby work with them too.
Does that help?