There is not much information provided so it is hard to say whether it is a good deal or not. Probably the main drawback with the bike will be its weight. I would guess that it is not light and probably weighs 18 kg+.

I would go round a few bike shops and see what they have to offer before getting one from Argos. Take the details of the bike with you and ask them if they have anything better.

I am surprised no one has said it already so I will be the voice of doom; take it carefully and slow riding on the pavement. It is statistically more dangerous than riding on roads (so they tell me), illegal and you will be responsible for any injuries to others or to yourself.