Yep 20K taxable, 5 yr RoS. So rough maths is 12K net. 12/5years is 2400 a year. 2400/12 months = 200 squidders a month for 5 yrs.
I think this will be enough to keep those who were already staying (waste of money as they were already staying). Will it entice those who were on the cusp of staying or leaving to stay, I would suggest not.
Those who have decided to leave, will it make them think twice - definitely not.
Problem is in 5 years will there be the pull from the civi world? It will certainly be harder to gain a foothold in industry.