I can only say good things about the trail-a-bike. They handle well, and are pretty manueverable, so long as you take it slow and easy.
It’s a big step up from the trailer or bike seat. Not so much for you, but for the kid. He’s got some responsibility now. I think most young children can handle it, too. They like it. They have to hold on the handlebars, they can pedal (and you can encourage them — it really does make a difference when they pedal or coast). They’ll complain about not having brakes.
Riding even short distances on busy streets will make you nervous. Once the two of you are used to riding together, it’ll be alright.
Of course, five-year-olds are not totally responsible. It does help to have someone else riding shotgun right behind you. Someone to say “Keep your hands on the handlebars”, “Don’t lean like that”, “Stop looking at me — eyes front” and most helpfully, “Keep pedaling”.
We had a bike seat once too, back in another lifetime.