I went out and looked at the "stuff" that came with the enlarger. There is an under lens filter holder. Is there any negative to using the filter under the lens relative to print quality? I will now search for a manual online so I can learn about the general workings.
Filters can fade over time, so you need to make sure your filters are still in good shape.
Under the lens filters are in the light path, so if they get sufficiently scratched or dirty they can impact print quality.
With respect to the "jerking around" observation, it is probably a reference to the potential of jarring or otherwise inducing vibration to the enlarger head when one adjusts the filter settings. That can be a problem if one is using split contrast printing.
My current enlarger has contrast controls in a separate control/timer unit, so there is no problem with it.
My other (currently in storage) Beseler Dichro 67 enlarger has filter controls on the head, so I have to be reasonably careful to rotate them without inducing vibration. It is sufficiently rigid to permit that, partially because of how one adjusts those settings.