Hi Stefan,
I'm not sure exactly how the function you are referring to worked in DrDepth, but it is possible to filter depths in RM by using the depth sliders in either a track view or the define map view of the project. Move the slider (upper or lower range), and track-points outside of that range will be greyed out. Click the Filter button (the funnel icon), and those greyed-out track-points will be deleted. It is easy to use this function to delete all points above or below a certain depth.
Matt