The remote control on the link will not work due to it works over RF (radio frequency) where the white nowtv box works over IR (infra red).
If you are looking at a replacement remote for your white box, then you will need a nowtv remote controller from either a white, black or smart nowtv box.
Alternatively you can use the Roku remote control App on an IOS, Android or Windows phone or tablet.
Welcome to the forum. That remote will work in theory for all the important buttons (home, back, play, REW, FF , star, etc, the shortcut buttons at the bottom obviously won't work) but I can't vouch for the build quality or reliability of that.
I'd recommend buying a genuine replacement from the Sky accessories store for £5 inc P&P
although as mentioned if you have an Android/iOS phone/tablet you could download the official Roku remote app for free and use that to control the box instead, if you prefer.
Edit: having said that if you have the White box currently it's getting pretty long in the tooth and slow now, rather than spending money on a new remote you might want to bite the bullet and upgrade to a new black NOW TV box instead.
Please ignore my previous post where i have given you some wrong information (my bad)
I totally agree with @Andy and would invest in a replacement black box where the white box is a little long in the tooth now and does seem to struggle with the more power hungry apps out there.
Should you go down the black box route, then make sure that your TV has an HDMI port (just in case you are currently using an ageing older TV set).
If you decide to use the Roku Remote App on your mobile device, then try to avoid any factory reset on the box, where you would need a working nowtv remote to initially setup the box again.
My original Now TV remote control was no longer working, but I found a One For All 8 universal remote in my spares drawer.
Using a Sat code 3061, the Universal works, although it has many more keys than the original Now TV remote. The basic keys OK/ Left/Right/Up/Down work fine and some of the other keys also seem to have an effect e.g. Menu, but I need to experiment to fully investigate what other keys might be usefully.
The One For All 8 universal remote is easy to get hold of, and cheaper than a replacement remote, even if you are able to buy one!
Hope this information is useful to someone?