Just want to add....
somebody told me...
500w good for those mostly walls, if you look at the wide wall, thats the one. those in corners are not.
700w needed for those hard concrete foundations of the hdb, for example, the ceiling, the beams, those seemingly vertical beams making your flat stand and not fall to the side.
i found this forum by googling for 'bosch vs black and decker' as i am planning to buy too.
both at 150$.
my contractor told me bosch is more user-friendly.
guy at diy shop said bosch parts can easily be replaced while bd needs be replaced entirely if broken; i dont know if this is true.
but i think ill get a bosch based on what i know so far.