My opinion is that you don't need it but it is cool
and I would quite like it. The nav directions appearing on the dash are good enough (and also cool) for me really but I like the idea of having my speed up there.
I read somewhere that someone found it distracting when driving at night. Would be much better if you customise it more: add and remove information etc.
Don't think cost of replacement is an issue in the UK as most insurance companies cover any windscreen with the same level of excess.