While it is far easier to mine than lunar ice, Mars ice still far more difficult to use than atmospheric CO2 on a first landing. My guess is people would have to land on Mars and experiment with using local water before building a mission plan around it. It could probably be used on a second mission though if enough effort was put into developing this resource on the second. The hydrogen currently planned for shipment to Mars for conversion Martian CO2 to CH4 and some oxygen could then be replaced by other mass. This resource could be exploited on the first mission to extend the amount of terrain explorable by increasing the amount of fuel available.

see ya