To be honest, I don't know. But the Terrain and the Urban Jungle are very similar in terms of chassis and are based on the same design. However, the carrycot mentioned (MB1-C1) was developed for the first Urban Jungle from before 2010. According to the information provided by Mountain Buggy, the carrycots are specially designed for each model. However, there is a table online at Mountain Buggy where most of the accessories are backwards compatible (i.e. old buggy and new Carrycot should work). But unfortunately I can't say whether the reverse is also the case. If the width of the chassis has not changed, then it should work, because the infant carrier adapter works on the same principle as the old Carrycot.

Yes, from what I've seen on the sites, it's brilliant. We're fans of mountain buggies, we've had the jungle, now we have the duet, the Switch and now the Terrain 3.0.

I can't answer that, as I use it without any additives.