To answer the question, they're pretty good for the money, always have a 'deal' on so tend to be similar prices per KG regardless of whether it's 25% off or 3for2 or similar. Quality is on par with more expensive brands, depending on what you buy, basic whey is plenty good enough for most people.
To perhaps explain kalneil's post I assume he is referring to the fact that most people don't 'need' protein shakes etc, they're not a magic bullet but will help you to hit your daily protein target if you struggle to do so normally.
This BBC show is worth a watch, it shows that if you're getting the protein in your diet then supplementing won't do much.
Creatine however, that's good stuff, and dirt cheap ...
http://www.jissn.com/content/9/1/33
I take a small shake (~20g protein each time) before and after workout because:
a) I can struggle to hit my daily target for protein otherwise due to work/lunch schedule.
b) It's certainly not going to do any harm.
c) It costs under 30p per serving so it's not exactly breaking the bank.