I put non folding Kojaks on my S6L a few weeks ago and they have been great so far. I find Brompton's own tyres to be slow like Marathons but without the puncture resistance. I haven't tried Green Brompton tyres for a while but I had sidewalls blow out out on them twice. Two of mine came with Brompton's own tyres so I have a few in the garage and I was trying to use them to save a few bob but I was spending it all on patches and vulcanising solution.
I got a BWR for my S6L because I got fed up with the lack of water resistance on the left hand side of the SRAM. The BWR (and BSR) have labyrinthine seals and a further dust cap on the bearings. The ball ring bearing might pick up some dirt, it has a plastic cage, but it's easy to replace. My oldest one, M6R, still uses SRAMs but I've got two of them so when one gets crunchy I take it off and put on the other one while I mend the dirty one.
I've got Stelvios on the S2L-X which are a little lighter than the Kojaks but Schwalbe don't make them anymore.