Hello Amazonian woman. Wow 600K!!
Obviously with the Nihola it's not very easy to transport to 'other places' to cycle. I mean, I know that's obvious, but it's something to consider. You do need to become more part of the traffic, instead of nipping in and out of it, with the Nihola. But I guess you're used to that with the trailer. Yes the head room, at least in the Nihola is high. I'd say you could easily put much older children in there.
My DD loves it. The thing is you have to be used to answering ALOT of questions about it. I live in the country and it causes a lot of looks and remarks (all positive so far but..). I often hear children see it as we go past saying "Mummy I want one!" Although that said, sometimes DD wants to cycle her bike and not be ridden but I just explain that's not possible at the moment over long distances. It's nice that we can go out on her bike, and when she gets tired, I can put her and her bike in the Nihola box. Like a suoourt vehicle...
Anyway to your Q. I drive it in town, on all sorts of roads, and along a woodland track. There's not City traffic though (I used to live in London so know what city traffic can be like, that said, it often moves slowly...). I've always been given a very wide berth.
I do know someone who has the Trio. I think she's the UK PR or something. She drives one in London. If you do come to London then it makes sense for you to test ride all three (do ring London Recumbents first to make sure they're expecting you and have the Kangaroo and the Nihola one in). Do you want her number (presuming I can still find it?)
The roll bars on the Kangaroo - I do see why you like them but have you thought about when they'd actually be used? This sounds like I'm trying to dissuade you from the Kangaroo and I'm really not. I nearly bought one. But it's a lot of money and I want you to be happy with your choice.
Good luck with the 600K ride and don't hesitate to ask anything else. I'm a bike bore...