This window will almost certainly reduce the effectiveness of the radiator somewhat. The real question is whether that ends up being significant for your application.
Others have suggested monitoring the temperature gauge--if the temp rises above the normal range, you've created a real problem. However, just because the gauge doesn't rise above normal doesn't mean you haven't created a problem (albeit a less severe one).
If your buggy has an electronic, thermostatically controlled fan, this fan will kick on whenever there's not enough natural airflow to cool the radiator. Generally this should only happen when moving slowly on a hot day. By installing this windscreen, you may find that your fan comes on more frequently, and runs for longer; or worse yet, runs constantly.
This would represent an extra load on your buggy's electrical system, and may lead to early fan failure.
The only way to know is to give it a shot with the windscreen. Monitor your temp gauge, but also monitor the operation of the radiator fan, if you have one. It may help to wire up a temporary indicator light that goes on when the fan runs.
If you need the windscreen, and you end up with cooling issues, maybe you can add some ducting to bring more air to the radiator, which may help offset the loss of airflow from the windscreen.