Well putting a HEPA bag in a machine really does make a huge difference!! Any A bag Hoover Convertible can get a HEPA bag and filtration from it will be far better than a standard A bag. A hard case bag machine can tell the results a little easier than a cloth bag of the dirt that can go through a vacuum bag.
Unfortunately many of the Hoover C and Eureka F&G bags that were vinyl dust clouds were possible. A lot of it depends on how well the bags are maintained and if one fusses with the dirt in the paper bag or knocks the vinyl bag into furniture during use. An ultra bright would show you some of the dirt that can be expelled from a vinyl bag using a standard filtration bag.
That being said, there are tons of current market machines that are near as bad!! Most bagless vacuums on the market to include Bissell, Eureka, etc. are filthy on the outside of the machine. The filth is not a result of the vacuum sitting out in a room on a regular basis, it is a result of terrible emissions from those machines!! Anyone who has ever serviced or used a Bissell PowerForce bagless, or Eureka Altima bagless or similar knows exactly what I'm talking about!! Remove the dirt cup and look how filthy the housing is around and behind the dirt cup, the entire back of the machine, the handle and of course the floor head. All of that is being knocked back into the air. Now comparatively as bad as I've knocked Hoover Type C and Eureka F&G bags above, I've never seen a floor head on one of those units look anywhere near as filth covered as these Bissell, Eureka, etc. bagless units and even bagged versions of the Eureka PowerLine Hardcase machines!!
A very good example of a pollution producing machine is also the cloth shake out bags of a Sanitaire SC886. I did commercial cleaning a year ago and the contract company I worked for had several of these units. Tons of dust clouds were spewing out of these units. Many of the vacuums had brand new cloth shake out bags too. But let it pick up some dirt and when that bag rubs along a desk or touches any obstacle while you're cleaning and a visible dust cloud will emerge!!
For great emissions I recommend a sealed system like a Riccar, Simplicity, Sebo, Lindhaus, Miele, etc. Filter Queen has terrific filtration, Rainbow has terrific filtration. Rainbow and Kenmore canisters both have earned Certifications by the American Asthma and Allergy Foundation. The Hoover Platinum series bagged upright with HEPA would have fantastic filtration. I have HEPA S bags in my 1990's/ 2000's Hoover PowerMax body style canisters. I have adapted a HEPA Kenmore bag to fit my Hoover Dimension 1000 vacuum cleaners. What's wonderful about the HEPA bag usage is not only the clean air to breathe but also how gorgeously it maintains the bag compartments of machines. I can't remember the last time I've felt the need to take a rag and the tedious time to wipe and clean a plastic body bag compartment in machines where a HEPA bag is installed!!!