In the bike pictured in LitePro photos the seat tube ends ahead of the bottom bracket shell, justifying the need for pushback for derailleur. In Brompton the seat tube ends behind the bottom bracket shell. So no, this adapter does not seem suitable for Brompton. As to the seat tube diameter, for other possible adapters you need to put some shim as well. One extra concern that I have about the JP8 model is of the mounting stud being seemingly secured to the clamp with only one small bolt that does not seem to go very deep into the material. Other Litepro adapters also came with one bolt but at least there as a threaded hole there for a second bolt, so you could make the setup more secure.

The linked Jetstream P8 seems to have a different arrangement around the bottom bracket, so I suspect that its identification as JP8 is incorrect. While I can find some other Dahons where the seat tube ends ahead of the bottom bracket, e.g. Bullhead, NBA083, IOS, I cannot find though any other 8-speed with a name starting at J. Talk about the garble of Dahon models! I wonder why LitePro does not finally make a dedicated Brompton adapter.