We’ve got a yepp, picked it up secondhand on eBay as wasn’t sure how we’d get on. Its great, my daughter loves being up front (she’s now nearly 2 and we’ve been using it since last November) and continually shouts go-go-go whenever we go out.
As above though, there’s a bit of a knees out riding position depending on his high you have the saddle. I have it a bit lower then when riding on my own to give me more stability when stopping. Not sure how useful the headrest would be though, my daughter tends to fall aslepp and lol to one side!
By the way, this is fitted to my 21″ specialized rockhopper 26er, it wouldn’t work on the London Road due to the dropped bars and a lower riding position.
If you’re anywhere near Epsom I’d be happy to fit it to your bike and you could try it out.
Dan