Your choice of gears is your own choice, but your photo clearly shows small front/small rear. When you snap the chain or break the derailleur or get horrendous chainsuck, you'll be sorry when you have to take your bike back to Evans!
The gear choice thing isn't about fashion, its about the usable range of gears. You could achieve the same ratio with a larger gear at the back and the middle ring. This would put less strain on your equipment and make that inevtiable trip back to the land of disappointment (AKA Evans) less likely. The advice given is meant for your own good. In that gear, your chain is not supported and more likely to flap around and damage your stays as the rear derailleur can't cope. The angle between the front and rear cogs is also too great, meaning that you are stressing your chain sideways beyond what you should. Nobody would criticise using the middle ring as your main 'pootling' choice. Most of us do, and it makes most of the rear cluster accessible.
This isn't meant to be a newby bashing post. Evans is an obvious choice for a first timer, and the Konas they sell (if that is what it is – looks like it) are the same as the Konas from any decent bike shop. Your choice of bike is a good one. Your choice of gear ratios is not, and your choice of retailer is not, but that comes with age, experience and the friendly, well-meaning jibing from STW forum members!