If you value your hearing spend the extra few pounds and do the job properly. I ordered these for myself and a colleague and having both used a lot of stihl equipment before we were extremely unimpressed.
Everything about the product is cheap and falls short of expectations. The plastic visor is flimsy and the lock in/out ear defenders neither stay in the out position or effectively expel the noise from tools. We tried these helmets for a couple of days, but in the end had to admit defeat and returned to the slightly more expensive, traditional Stihl Peltor supplied units.
Possibly suitable for garden use ie hedge trimmers, but by no means a real alternative for the regular user and simply does not deserve it's Stihl branding.
Go for the 'Beech' or 'Birch' units for the extra pennies.