Okay "proven technology" is an argument I can buy, but: the tikit not only has internal hub options, it has more and better internal hub options than the Brompton. Plus it has fixed and derailleur options too. And how exactly could one frame size possibly be construed as an advantage?
The draw for me to the Brompton is 1. Internal hub gearing (I gave up on the deraillleur system some time ago), 1. one frame size (I seem to be between 2 sizes for the multi frame selections), and 3. proven technology (it is based on the old classic Mini Cooper of the 1960s with it's rubber cone suspension system and handling characteristics) plus as you pointed out earlier the accessories really do add to the bike. The tikit does have it's appeal too, but not enough for me and my style of riding.