I am sure that they could be fine, just wanted to make a well informed choice, was not assuming I would have to flatten ;-)
I fell now i can indeed make a very informed choice.
FWIW i took my £10 B&Q stanley SB3, and now that i put the iron in bevel down, (i swear i bought it with the bevel up), and i had already scary sharpened, i proceeded to try to flatten a (very) uneven and rough board by hand, first board flattening of my life by hand.
got the depth to take decent amount, think i had the iron parallel in horizontal way, got it pretty good, few edge gouges where you'd have camber on a plane for that normally, took it down to "wafer" and got it really smooth, was surprised by how flat it was, slightly high in middle, perhaps 0.1mm, soon sorted that, amazed and happy...
then I did the other side, and it all went wrong, huge gouges, i would set depth, find i was getting nothing, change it 1/8 of a turn (less than 1/64") and suddenly take 3m out and get jammed in, then move up, get it about right, and suddenly after 2 strokes nothing again. that side was not so lumpy to start with, however it really felt like the iron was moving inside the plane depth-wise. (I had checked the grain orientation, however was almost dead straight along board, which was about 12" long). So went from ecstatic to depressed in about 10 mins flat.
One very key advantage of hand planing over machines i can clearly see now though is the ability to have a beer whilst you work ;-)