The fretboard on the bass is open-grain Wenge and, having just turned it fretless, I didn't want to start chewing up the fretboard with roundwound strings. Was also interested in what people were saying about flatwounds making a bass naturally sound a bit more like an upright in tonality, which is what I was after with this one. The roundwounds sounded just fine, but wanted to experiment.
Happy to say I've had a set of D'Addario Chromes on there now for a week and they sound perfect. Another benefit I've noticed is a complete loss of string noise when sliding notes. Everything is just so buttery smooth I'm one happy bassist with how this instrument has now changed and turned out. Inspired to practice my fretless a lot more.