The idea is pretty neat imo. Its a simple mechanism. Over the long term I suspect it may even be cheaper to use the robot cause the robot does not need to be fed or managed. I'm tempted to build one myself as the parts cost doesn't look like it'll exceed $1.5K. The music in the video though...
So depending on the monkey the robot may be cheaper.
Another cost farmers will likely look at is the cost of a monkey handler, which are widespread vs the cost of a specialised employee who can operate a robot. Unfortunately, the monkey handler is likely cheaper.
As far as i know training this monkeys takes time, the robots will do the job right away if you put this in the long term the robots is cheaper than keep a monkey. But of course they should make it simple in the way that a non specialized employee can operate the bot without any problem.
According to https://www.wfft.org/wildlife-general/a-growing-trade-monkey... monkeys cost between $1000-$4000/head
Also do note that monkey based coconut picking is on the decline: https://www.pri.org/stories/2020-08-26/does-thailand-have-mo... Only a small proportion of coconuts are actually picked by monkeys.