It came today and it's brilliant!! 
This is it
Easy enough to fit that even I did it in 5 minutes flat.
Takes less than a second to put on/take off once it's fitted.
Just did a few laps of the car park with Junior Dog and even though it was our first time (and I've only recently - like in the last 2 weeks - started riding a bike after YEARS of not) I didn't feel off balance. Managed figures of 8 and so on, so straight lines should be a breeze 
And she'll be able to pull me up the hills! 