Just watched the recently released Kakushigoto compilation movie. It somehow compressed the TV series into a roughly 80 mins long film. It showed almost all of the beginning and ending part, and skipped a lot of the middle part if I'm not wrong. The extra scenes were added to give vital information about Hime's mom and to stretch the ending a little bit. One of the main problems of the TV series was the rushed ending, but this movie tried to fix that. I would've liked the duration to be longer and more scenes from the TV series to be added, but I still liked it a lot and got emotional just like as when watching the TV version.
Recommended for those who liked the TV series. And no, it cannot be used as a substitute to that.