Good price for a helmet. It has all the CE marks so should be fine for most people. Free specific day delivery & 1.57% Top cash back. 34 positive reviews on Argos website - 4.6/5.
Product description / spec from Argos Site:
This smart looking Women's helmet has foam padding and 10 air vents for comfort. A secure fit for head sizes 58 to 62cm making their bike ride much safer.
10 air vents.
Head size from 58 to 62cm.
Quick-release buckle fastening.
Was on here for 3.99: http://www.hotukdeals.com/deals/challenge-bike-helmet-ladies-3-99-argos-1927551
I also got 8% back from Halifax Rewards (£0.24) Plus 1.57% TCB.