I bought the Tesco pump for a quid, I assume they are similar, my friend used it, in the rain, one taxi ride later and they got home swearing their revenge on it. The thing wouldn't stay on the valve for them, I however of "clamp hands" fame managed to keep it in place AND fill the tube. however it wasn't raining and cold, nor was I outside and tired when I tried it.
since then it disintegrated without physical assistance, I honestly doubt it would have stood up to being dropped.
When you REALLY WILL depend on something, its worth spending the money.
poundlands Hi viz jackets are an ok purchase though I hear.