If you have a rounded edge, it means it has been maintained with an abrasive that is not aggressive enough. You'll see this with any razor maintained with pastes alone - a visit to some proper hones would take care of it. Now, before I sound judgmental, I do the same with my razors. I use pastes until the shave quality tells me I need to do something more. In fact, every time I feel the need to go to a double-edged razor I now know I should reach for a Shapton rather than a Merkur HD. It was easier in the days when that choice didn't exist! Every razor needs to be properly re-honed now and then.
Chris