Longtime Aperture user here. Recently converted to Mylio and loving the speed so far. One feature I really miss is the ability to geotag photos based on a GPX track from within the app. This involves importing the GPX track, then assigning coordinates to photos based on their timestamps.
After trying many 3rd party utilities, Geotagster comes closest to doing what Aperture can, but it’s not very convenient since Mylio needs to re-ingest the XMP.