Dave

i have used fast flex on alot of occasions i.e. floating floors ( plyed first ). dont get me wrong i always use bal products and have done for many years.... but the thought of tiling onto brand new softwood floor boards makes me cringe... they haven't become accustomed to room atmospherics if laid new for tiling..causing them to twist and shrink slightly... this is not an overnight process...
My problem i suppose is i'm what you call old school tiler.. i use new products and old methods aswell......fastflex does work on floorboards i know but there is nothing wrong with just making sure....peace of mind i suppose.....
plus another thing to weigh up is the cost of fastflex against plying out......i can ply/fix with normal flex cheaper than using fastflex alone......but every one has there own preferance's........dave....