I started off by measuring the Shark ICZ300UKT’s raw performance in AirWatts (AW), which is a combination of suction power and airflow. On Eco mode, I measured a result of 35.65AW, which is similar to a lot of handheld models; 56.98AW on Standard is similar to your average cordless; and 175.24AW on Turbo is a lot of power for really tough jobs.

The device has a couple of main controls. A thumb switch on the top is used to turn the vacuum on and off and swap between hard floor and carpet modes. With carpet mode selected, the rollers spin faster to agitate the fibres more and clean deeper into the carpet. This doesn’t alter the suction, but you can give it a boost by pulling the trigger that sits just in front of your forefinger as you hold the handle. Giving the dust bin a wipe to properly eradicate dust inside is a must with all bagless vacuums, and I've found that you probably only want to go about a month before you give a deeper clean to this vacuum. That's because the sensors in the CleanSense IQ head will stop working if they become clogged with dirt or dust, and you'll lose one of the merits of this very expensive vacuum. Comparison

How we tested

Like many of Shark's corded and cordless models, the IZ300UK is fitted with a flexible cleaning tube called Flexology. This means the vacuum conveniently slots underneath coffee tables and sofas, helping you clean those hard-to-reach areas. In the box, Shark has been very generous with accessories. You get a crevice tool, a multi surface brush (hard brush and upholstery tool), mini pet brush (great for carpets and sofas) and the anti-allergen brush, which you can use for dusting pretty much everything from blinds to furniture thanks to its articulated joint.

Shark is well known for making hugely flexible vacuum cleaners, and this continues through to its cordless models. As with previous Shark cordless vacuum cleaners, the IZ251UKT has Shark’s Flexology technology. This enables the wand to fold over in half, letting the vacuum stand up by itself so that you can easily wheel it into a cupboard for storage. It’s a shame the IZ251UKT isn’t able to stand up unaided when fully extended; the weight of the battery and bin tilt it over. This vacuum cleaner comes in about average for noise, at 67.5dB on Eco, 72.6dB on Standard and 75.6dB on Turbo. You can clearly hear the Shark ICZ300UKT and can’t really hold conversations over it, but it isn’t so loud as to be annoying.With its 4.58kg weight, the Shark IZ320UKT sits about in the middle of the cordless pile, balancing weight against power. I found it very easy to move around, with the floor head dashing around carpets and hard floors, and the LED headlights helping in darker areas.

It comes with just two accessories: a crevice tool and a two-in-one upholstery nozzle and dusting brush. Lots of premium cordless vacuums come with several more accessories, including a mini turbo brush - which is handy for giving awkward spots a thorough clean. As I said before, it delivers where it really counts, thanks to a powerful motor, large dust capacity and effortless movement around the house. Still, it’s quite a bit more expensive than a Gtech Pro 2 and equivalent Hoover H-Free, but cheaper than a Dyson V15. On balance, I think the price reflects the performance, and all things being equal I’d choose this over its rivals for those removable batteries and clever elbow joint in the tube. The fact it happens to be really powerful and agile makes it even more convincing. Verdict The dust bin on the Shark Stratos IZ420UKT is fairly small, at 0.8litres, meaning that those looking to clean areas that are far away from their main bin might struggle. On the flip side, I think that making the capacity any bigger risks ruining the sleek feel of this vacuum, and I'm happy that SHark has kept it smaller.I then combed cat hair into the carpet and ran over it using the standard power setting. Again, everything was collected with ease. If you've read this far, then you might have gauged that I am a huge fan of this vacuum, and that I'd tell anyone it's a worthwhile investment. I test a lot of different vacs, and this is the one model that I've fought to keep in my flat (even though we definitely do not have room for it!). It really is unmatched for me in terms of suction power, and I've grown addicted to those clean vacuum lines it leaves in my carpets.