300 GBP converts to almost $500 Canadian - I think you can get a reasonably adequate entry level hybrid from a bike shop for that money here. A truly bottom of the barrel BSO from a big box store would actually be a lot less.
Anyway, as has often been pointed out, much of the risk from a box store bike lies in who puts it together. A friend of my husband was nearly killed some years ago when the brakes on his brand new Zeller's* bike seized up solid the first time he ever really tried to stop hard at the bottom of a hill. They'd been improperly installed in the store.
(*A Canadian el-cheapo chain, since bought out by Target)