you need to be careful with all jointing products on porous sandstone or they will all stain the surface
bottom line is this loydE1, you asked a question and we can only give you our experience of using a variety of jointing products, you can't say because the BAL technical department said its the right product to use therefore all other products are useless as that does not stack up in the real world (if you can show test results for this then that's a different ball game)
all companies carry out tests on not just their own products but other manufacturers and suppliers too to see if their own products are as good, this is done in a controlled environment and not in a variety of locations like for example a north facing garden adjacent to a 20 foot high conifer hedge what is prone to secreting a layer of green slime over the surface of the paving, you use any buff jointing product and it will turn from buff to green to black in only a few months - especially in the costa del north west where it rains every other day
from this experience we now only use the grey jointing products