I know nothing about x-line brushes but I've found out early on a chepo flocked car brush is ideal to dip in a bucket of tfr mix etc to pre soak and brush over baked on grimy surfaces like badly soiled guttering, fascias, soffits, bargeboards, cladding etc.
Flocked bristle brushes seems to me to hold in more chem and removes surface dirt more easily than using a mono filament/unflocked bristle brushes.