Smartphone users tend to lie in one of two camps when it comes to screen protectors: they either swear by them, or they don't want one at all.

If you care about protecting your screen from scratches, you'll probably already know that you can pick up a pack of screen protectors for a couple of quid from Ebay. However, while you can consider them disposable, they leave much to be desired in the quality stakes, and can be hard to apply well.

Tech21 - purveyor of smartphone, tablet and laptop cases - reckons it has come up with the perfect solution: an easy to apply screen protector which is optically clear, is self-healing and also disperses the force of an impact to reduce the chance of your glass screen shattering.

The Impact Shield is a bit cleverer than your average screen protector as it has three layers. A hard top layer spreads the force of an impact and has a scratch resistant coating.

Tech21 Impact Shield diagram

In the middle is a so-called BulletShield layer. Tech21 worked with chemical company BASF to develop this optically clear polymer which absorbs impacts - it's similar to the stuff you'd find in bullet-proof glass.

Last is the soft base layer which also helps to absorb impacts and has an adhesive backing to stick to your smartphone or tablet.

In this respect, the Impact Shield is barely any different from the majority of screen protectors out there: you need a perfectly clean screen to avoid bubbles caused by dust or debris when you apply it. Moshi's iVisor XT screen protector avoids this problem by having a sticky border, but no adhesive over the actual display.

As long as you make the effort to damp down your work surface and ensure your screen is completely clean, it's possible to fit the Impact Shield with no bubbles at all. As it's quite sticky, it's not easy to remove it and reposition it - Tech21's instructions warn that you might permanently damage the Impact Shield if you remove and replace it too many times.

Tech21 Impact Shield Galaxy S4

It's cut fairly conservatively, so it doesn't go right to the edges of the iPhone 5 - for example - but it isn't designed to protect the edges of your device. For that you'll still need a traditional case. Tech21 makes a range of cases for popular smartphones and tablets. We found that the size of the Impact Shield for the iPhone 5 was perfect for cases that slightly cover the front edge of the smartphone.

Where the Impact Shield could earn its keep is if you ever drop anything directly onto your screen. We were shown a demo of a ball bearing being dropped onto an iPhone 5 with no protector applied; the screen shattered on impact.

The same ball bearing dropped from the same height onto an iPhone 5 with the Impact Shield installed escaped unscathed.

Plus, when we attacked the Impact Shield with a wire brush the faint scratches disappeared almost instantly.

We're told that the Impact Shield won't ever yellow as some cheap screen protectors do, and were pleased that there was no oil-slick effect as we saw with the iVisor XT. In fact, it was impossible to tell the difference in terms of screen quality between two iPhone 5s - one with an Impact Shield and one without - as long as you covered the big cutouts around the home button and camera. It's that clear.

Tech21 Impact Shield iPhone 5

Tech21 Impact Shield: bottom line

The Impact Shield is a good screen protector that does its job well. It isn't the easiest to apply perfectly, but once installed you'll hardly notice it's there. It isn't cheap, and it isn't really re-usable, so it falls down on value compared with the Moshi iVisor XT. That screen protector, however, suffers from an annoying oil-slick effect which is enough to put many off.

Currently, the Impact Shield is available only for a small range of handsets including the iPhone 5, Samsung Galaxy S3, S3 mini, S4 and Note II (all £20), plus the iPad mini (£24). The 9.7in iPad version won't go on sale for a few months, and you're out of luck (at the moment at least) if you own a Google Nexus or any other device.

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