water filtration machines and newer tristars
Interestingly, the current water filtration machines are about 40 years behind a lot of the other machines that are available, at least as far as raw cleaning power goes. One way you can compare the actual power of a vacuum is to connect a turbine brush and see how fast the vacuum is able to spin it. While mhy Sirena is able to spin a turbo brush slightly faster than my Rainbow E2 black, both machines spin it about as fast as an Electrolux 1205 or Compact C6. I think the motors in these machines simply do not spin as fast as other current vacuums, this could be because they have a separator, not sure. The main reason that Rainbows are so expensive new is because they are sold door to door, so everyone needs to get a portion of the sale. The Sirena, although it has some differences, cleans just as well as a rainbow, but since it's sold on line or through vacuum stores, it's about a third of the price. Remember that as long as it has enough power to remove the dirt from the surface, it is doing its job, but if having the most suction and airflow is your top priority, I would say a water filtration machine is not for you, you will be disappointed with the results. That said, I enjoy both of my water filtration vacuums and think they clean very well.
Regarding the Tristar machines, I have a Miracle Mate and I'm pretty sure it uses the same motor as the Tristar CXL, I've also heard that this motor is used in the Metropolitan machine which I also have. My Miracle Mate is very powerful, so I would think the Tristar CXL would be as well. I think Aerus ruined Tristar when they purchased them. The quality is not as good, they no longer use the two stage motor, and the hose end and electrical connection are nonstandard now. Interestingly, the bags made for the Miracle Mate are closed bags, but I use the Tristar bags with mine since they are open, and an open bag will provide better airflow, at least in theory.
Mike