There is a good percentage on the upper end of the experience spectrum that just won't take a coding challenge as part of the hiring process. You will miss out on a huge pool of talent that will automatically opt-out before the process even starts.
This ... I have a personal rule, I never interact with bots in a professional capacity (it's a sure fire strategy for demoting yourself to a cog in a machine), this includes slackbots etc. I would certainly not interact with a bot for a company I don't even have an business relationship with yet.
