If so make sure you order the non smart remote which doesn't have the voice search etc.
Ebay should be fine if you buy from a trusted Ebay seller.
Also there is no guarantee that the remote is the problem you could have a dodgy box or IR receiver on the box.
You could try this simple exercise to see if your existing remote is blasting out IR commands.
First, try removing the batteries from your remote and re-inserting them. If that doesn't work, try replacing them.
Help tipIf you've got a smartphone with a camera, you may be able to use it to see whether the remote is sending an IR signal or not. Smartphone cameras can 'see' a wider range of light wavelengths than the human eye, including infra-red light. This will generally only work on smartphones with a front-facing camera:
Put your smartphone in camera mode as if you were taking a self-portrait (you should see yourself in the camera).
Hold the remote control in front of the camera and press buttons on the remote.
If you can't see the IR signal flashing as you press buttons, then try replacing the batteries in the remote.
If you wish you can use your smartphone has a remote by downloading the free Roku Remote App from your phone's App Store (please note the Roku App works over WiFi and not IR like your nowtv remote so this doesn't really prove that your nowtv remote is faulty or not).