Direct export to android calendar (not via Google Calendar)
There are third party apps (e.g. IcalSync) that can import calendars from a url directly into the android calendar, but it does not seem to work with the url that Todoist provides. Importing via Google is a rather slow process since Google's server does not seem to import my Todoist calendar more than once a day.
Importing my Todoist tasks directly into my Android calendar would be a nice feature of the Android client!
A possible solution would be to directly add the Todoist calendar into the My calendars section of Gcal (via API). These seem to be updated almost in real-time (an example of this is the Doit.im Gcal integration)
The iCal feed works with any calendar software that supports this standard and can be used directly with it.
Yes, now it works. It seems that the URL had been corrupted when copied to the iCalSync app. On restoring it everything works fine!