I've got jobs with bars, but hasn't been a problem as I can angle a standard 10" vikan behind the bars.
A standard kitchen floor brush would be fine, though you would need to make space for the jets.
I think there is such a small market for a brush of that size, that it wouldn't be worth it to produce one specifically for our line of work. If they did you would be looking at a stupidly high price.
I agree that the Vikan is well suited for this. I find its the only brush I have found that doesn't need an angle attachment. I use an unger ali pole for this job and a Vikan to Unger straight adaptor. I use the ali pole as I don't want to damage my carbon fibre ones on the steel grilles. Trouble is that the combination is so heavy when trying to guide it into the grilles of balconies on the second floor.
Have never tried the superlights.
I recently spoke to a window cleaner who was doing a block of apartments in town with his 57' and he says that he has negotiated with the management company that the tenants clean their own juilette balcony doors as they open inward - he does all the other windows and charges accordingly.
Whilst that may not work in Spain with all those spanish bars, it may be worth while considering here as an option.
I got an 8" Vikan swivel brush and its a total waste on money - it isn't a 'true' swivel as we know it and it takes too long the clean through the bars as it isn't wide enough IMO.
Spruce