They are compact upright vacuum unit, do not have any attachment, such as dusting brush and crevice tool, for above floor cleaning.

image from manufacturer

The 2 main differences between Shark Rocket Powerhead AH400, AH401, AH452 and AH452W are the wand and headlight.

Headlight
The AH400 and AH401 does not have headlights on the nozzle whereas the AH452 and AH452W have center LED headlight on vacuum head.

Wand
The AH400 and AH401 come with a non-telescoping wand.
Whereas the AH452 and AH452W come with a 4 position telescopic wand which can be adjusted to fit user height and for compact storage.

Cord Length
Cord length ranges from 25 feet to 30 feet.
The AH400 and AH401 cord length is 25 feet versus 30 feet on the AH452 and AH452W.

Dimensions
Dimensions of AH400/AH401 are 45.3″ x 12.6″ x 12.2″ (H x D x W)
Dimensions of AH452/AH452W are 44.9″ x 12.6″ x 12.2″

Color
The Shark AH400 is purple, AH401 is green, AH452 and AH452W come in blue.

Included Brushroll and Holster
All of them come with a removable and rinsable deep cleaning all surface brushroll.
The AH401, AH452 and AH452W also come with an additional Gentle Touch hard-floor brushroll that is designed specifically for hard-floor cleaning and a on-board brush roll holder that can be attached to the wand and store the brushroll. The 2 brushrolls are interchangeable.

The AH452W is sold directly from the Shark, it is the same as the AH452 that is sold from retailers.

Below are the links to download the manuals from Shark official site, you can get more detail by reading these user guides.
http://www.sharkclean.com/include/pdf/manual-AH400.pdf
http://www.sharkclean.com/include/pdf/manual-AH401.pdf
http://www.sharkclean.com/include/pdf/manual-AH452.pdf
http://www.sharkclean.com/include/pdf/manual-AH452W.pdf

If you know more differences between these Shark Rocket Powerhead vacuum cleaners, please share by commenting below.

Some QnAs you may want to know.

Can you turn off the brushroll when cleaning hard floors?
No.
Is the brush adjustable for different carpet piles?
No. There is no manual adjuster. But the vacuum has 2 brushroll speed settings on the handle.
Is there any suction control?
Yes, there is a Suction Control Button on the Motorized Floor Nozzle.
Does it have a auto cord retractor?
No.
Is there any tool for corners or above floor cleaning?
No, there are no attachments except for the optional “Holster” to hold the extra floor brush, the Shark Rocket Powerhead is supposed to be used on floor cleaning only.
What is the amps?
The power specifications are 120V., 60Hz, 600W, 5A
Does it have a HEPA filter?
No.