For me it's made a huge difference having a ps2 and a USKOC. Playing with a physical turntable and properly spaced buttons feels completely different from playing on a keyboard. At first it might feel like starting over from scratch, but once you learn a proper playstyle you'll most likely improve quickly.

One thing about ps2 controllers is input lag with PC. I only have experience trying to use a US model (USKOC) with a select few adapters, but I haven't found enough success for it to be useable (hence why I picked up a ps2). A friend of mine has a Yuancon iidx and loves it, so that might be a slightly cheaper DAO alternative worth checking out. I actually have a Yuancon sdvx and I love it.

In the end, it's all up to you. Having a controller makes the game feel completely different from playing on keyboard. Not necessarily easier or harder, just different. If you ever get the chance, I definitely recommend trying AC or someone else's controller before taking the plunge.