Johnny's isn't good. For dishes like split pea soup, I recommend a visit to a Swedish apothecary in the month(s) before Christmas and Easter -- they have a great mustard which is particularly good for traditional food, and also (together with a creamier one like Graveleij and a little bit Dijon) great for mustard herring after my grandfather's recipe. :)

Just so I got this right, pharmacies in Sweden sell their own mustards? Or is an apothecary a different thing there than a pharmacy?

"An unusual tradition - a hangover from a time when people used mustard for its medicinal properties - is that chemists sell julsenap at Christmas"

First hit I got: https://www.totallyswedish.com/products/johnnys-mustard-410.

Ikea generally sell mostly their own brands, at least here in Sweden.

I'm in the US.