It had a technical halt at DDS the last time I traveled. If you are going to see the falls from Castle Rock or Londa, then take a return ticket from Kulem to Castle Rock or Londa beforehand. It doesn't halt at the falls as far as i remember, but no tickets are issued at DDS and ticket checking for tourists and trekkers boarding at DDS is quite strict now. So take a to and fro ticket or whichever is possible.