I have 3 cogs on my BWR and mounting required only either original Brompton parts or parts common for all bikes. You do not need the expensive Ti Parts kit and, if you need a kit at all, you can get an inexpensive one from bikegang. Yes there was tweaking involved, but not particularly different from other bikes - usually when you mount something new on a bike there is some mismatch of one type or another and you deal with it.