It's the caveat emptor I'm afraid and with all exercise equipment you really do get what you pay for. It's not just functions, but the durablility and strength of the equipment.
Argos tend to do the standard cheaper equipment and the mid range. They aren't the best quality equipment you can get. The Elverys range is more mid range.
Both are suitable for beginners and light exercise, but I wouldn't be planning on training for the Tour de France or anything.