I don't think using a pen will hinder your quality. For me, using a pen is infinitely easier and produces higher quality sketches. Although I think ballpoint pens aren't amazing for sketches, - try pilot pens or the like, they enable a flow of ink without the need of pressing on the paper. This is also why I prefer pens to pencils, for example. Also, the fact that I don't have the possibility to erase helps me move forward and make more sketches, regardless of small mistakes that I can't help but erase when using a pencil.
I hope this helped, this is just from my personal experience.
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