Just looked at the trailzilla routing page, and must say the OS mapping is great considering its free. Its on a large area too..
I looked at Trailzilla after your mention of it, as it is a new one to me.
Not sure why you say it's on a large area, as the home page has side bars left and right, leaving a much smaller area of map to be viewed. It reminds me of the old StreetMap with the little bit of map in the middle.
Unless it is full width on the routing page that you specify?
Well I never got to see that, because after the fiddle of registering I tried to look at 1:25k but I was instructed to go to My Trailzilla, where there were more boxes to tick.
At this point I opened another tab on my browser (I had just received an email notification) and then went back to Trailzilla, which again told me I needed to sign in but when I did, it told me fernman was already signed in on another computer??? and I needed to sign out and come back.
That was my first and final experience of Trailzilla. It might be OK for some people but it's too much hassle for me. I can open Bing any time I want without having to sign in, I can look at anywhere and in whatever scale I want, plus it is full screen width.
Edit: I just read the Welcome email I received, which was from SALES@... (my capitals) and it looks like I'll be receiving regular emails from them, no doubt trying to persuade me to pay for things. The only thing I haven't found anywhere is how to cancel the registration, short of using their Contact form.