Nichicon Muse are BiPolar caps, most caps are Polar, they have a negative stripe down one side, you can't interchange the two.
They are good as coupling caps etc.
My favorite Polarized caps are Panasonic FC's, Elna Silmic II are well regarded as well, but they are bigger and more expensive.
I've been mostly buying Nichicons from Mouser when I've needed electrolytic caps lately. They made a ton of grades. The top conventional ones for audio are (in order) the KZ (Muse - these are black with gold printing), FG (Fine Gold), KW and FW grades. For bipolars, they have ES (the green Muse ones). Nichicon doesn't make every type in every value, and I don't think Mouser carries all the ones they do, so I just try to pick the best one they have in the value I need.
I'll use these in both audio and power supply circuits.
http://www.nichicon.co.jp/english/products/pdfs/e-es.pdf
According to the specs, Muse are non polarized.
Generally speaking you can't replace a non polarized cap with a polarized one. But you can do it the other way, replace a polarized one with a non polarized cap.
So, I'd check the application of those bi-polar caps, to see if a polarized one is OK in that place.
I've been happy with the Nichicon audio caps and the Elna Silmic II also. If I were to go out on a limb I'd say that the Nichicons are a tad brighter than the Silmics (to my ear) but that is just a generalization based upon my perceptions in my system using my ears, so hopefully nobody get's their panties in a wad over it.