Any coolant for a "mixed metal cooling system" should be fine. It is worth investing in decent coolant. The difference really isn't that much and you really don't change it very often. Wrong or bad coolant can however lead to corrosion, which could then cause the thermostat to stop working or things to clog up.
I would usually recommend against buying anything from Hellfords. It's often not actually that cheap and the quality is crap. Go to a decent parts shop. They'll probably be able to get you what you need for a decent price.
