A couple of trips to the swimming baths, a club ride (family friendly section) along the canal & a picnic to the park all were spot on. Frank was just over 14 weeks old on his first venture and fell asleep quickly.

The trailer is very light weight, although where we live is considerably hilly and on the ups it's certainly slower, although on flatter terrain you don't know you're hauling anything behind you. Storage space is spot on for baby gear, d-locks & picnics.
We love it!!!
But I have invested in a Yepp mini front seat for when Frank can sit up on his own to enjoy narrower paths. I'm looking forward to longer adventures with skinnier tyres and more varied terrain, which may be beneficial for commutes and dropping Frank off at the childminders (depending on how the work restructure goes - I may or may not have a job to go back to, but trying not to let that thought spoil my time off with Frank).
I think the cargo bike project might be off for now and we'll see how the trailer & seat go for now.