Well, from testimonials it sounds like the clothing isn't for killing insects that get on you so much as for repelling them from coming close to you in the first place. I don't know if it's hype or not but supposedly it repels them enough that you don't need all of your body to be covered. Like having a hat and shirt will protect your exposed neck and face too.
I've been bitten by mosquitoes through my clothing. I don't know if I smell so tasty that they put extra effort in trying to snack on me. T-shirts won't protect me where the shirt lays close to my skin, like on the upper shoulders, back, and chest. And button shirts are too uncomfortable to me in the summer. I need the stretchy knit weave material that T-shirts are made from. Unfortunately those fabrics offer the least type of protection. But I've even been bitten by mosquitoes through a pair of jeans, which surprised the heck out of me until I realized that their proboscis probably are thinner than the jean's weave.
So if these clothing actually repel biting insects within a certain distance instead of just repelling on contact, then they'd be totally worth it for me.