Has anyone with a mountain buggy purchased the car seat adapters and if so, are they worth it? I have a mb urban single, ds2 is 3 weeks old and I'm thinking it might be useful to put the car seat on the frame for quick trips rather than move him from the car seat to the carrycot and back again. But the instructions make it look as though you can't leave the car seat adaptor on the pushchair, which sounds v.tedious. I doubt I could be bothered if that's the case & the adapter is 40 pounds, so any light shed would be really helpful, thanks!