I think the key thing here is that if you are comfortable in downloading the tool to enable Windows 10 to be pushed through to your device early, is that you run the risk of hardware not functioning properly. There are loads of posts around now whereby users are having issues with video cards etc and not displaying correctly.
If you decide to force the upgrade, you will have the option of reverting back to your previous OS, but this is time consuming. Bottom line is, if you are not sure, leave it and the prompt will come once drivers have been updated and that your device is now ready to install Windows 10. Although it's a free upgrade from certain OS's, this is running for 12mths so no rush.