Hi,
Yes you can use CumulusMX without using Weatherlink. CumulusMX saves the monthly log in MmmYYlog.txt format which can be read/opened by most programs including Excel, and at whatever logging increment you set, i.e. 1 min, or 5, 10, 15, 30 minutes. Be careful, don't reverse save from Excel to .txt as then the files may not be valid in CumulusMX. 5 minute interval gives about 17 days before the logger overwrites so twice a week is well within a 5 min interval and your twice a week download.
You set the logging interval for CumulusMX data files in CumulusMX and that interval should be the same as the Console/logger is set. Otherwise Cumulus won't know where to start in doing the archive catch up and therefore will download the full logger each time you start CumulusMX. Console/logger interval is set in Weatherlink.
Enjoy,
Paul