The difference between Bissell 82H1 and 21K3 are:
Bissell 21K3 vs 82H1
images from manufacturer

Air Flow Indicator:
The Bissell 21K3 features Air Flow Indicator that monitors air flow to let you know if a clog occurs whereas the 82H1 does not have the air flow indicator.

Warranty:
The Bissell 21K3 carries a 3-year limited warranty while the 82H1 has 1 year limited warranty.

The similarities:
* Both of these 2 Bisell upright vacuums do NOT feature brush ON/OFF control, the brush keeps spinning.
* Comes with 27 feet cord, without auto cord reel.
* Weighs 16 pounds.
* Features HEPA Media Filter to help remove tiny particles.
* They are bagless.
* Has 5 height settings for cleaning different types of floors.
* Features Dual Edge Cleaning for cleaning places like baseboards.

Please reply below if you know more difference between these 2 BISSELL Cleanview upright bagless vacuum cleaners.