If your a new rider and not capable of doing your own basic bicycle maintenance then I definitely recommend that you only buy a name brand bike from a local bike shop that will support you with checkups and after sales service.
$400 isn't expensive for a basic new bike in my book in Australia anyway. They may be cheaper in the USA. What's the price on a Giant where you live?
Really cheap bikes won't necessarily outright break on you but the gears and brakes can be difficult to adjust and if you don't know how to adjust the brakes and gears yourself yet they always need adjusting then you can see how cheap bikes just get left in a shed or abandoned.