Might be location specific but out of 300+ candidates for 15 positions mid to senior level over 8 years in London recruited using this technique I've only ever had one person turn it down. We ask for fairly simpler requirements and for people to limit themselves to 4-6 hours over the course of a week with a focus on comments and recording their thoughts in a readme to suggest how they'd scale things if it was a real project. We don't really bother with many technical questions outside of the project anymore. It really is the single most important thing to get a glimpse into a persons ability to deliver, let them code at their own time in a setting they are comfortable with and then do a peer review with them on location and discuss the implementation and potential enhancements. The rest after that is generally just team fit and culture alignment checks.