The hub is basically the same - Brompton used the SRF-3 from 2005 until about 2010 and then rebranded it to BSR (Brompton Standard Range), probably to have a more stringent naming along with the 6 speed BWR (Brompton Wide Range) hub they introduced in 2009 as follow up to the SRAM based 6-speed (and until 2005 as the three speed as well). I am not aware if there have been technical changes to the internals als well but do not think so. Anyway a switch from SRF-3 to BSR has no issues or implications.