I didn't mean to say that Avalir cleans better than Sentria (and I agree the Avalir IS Sentria with a different trim). I meant that IMO Avalir doesn't clean any better than Diamond, or even Heritage line. Kirby found a great system, and they just keep repeating it with different cosmetic "improvements". Over decades (century!), they did improve, but materials, and technology improved a lot too, as a whole.
Kirby is still straight air intake machine with side bag. "Tech Drive" was somewhat an improvement (for some people), but the models that have it, are only marginally easier to push than Heritage line. Because the rear wheels spin with the same speed, I actually find Heritage 2 easier to maneuver. I can use the G series without engaging the transmission, but it's MUCH harder to maneuver like that (especially in the tight spaces), than Heritage 2 as is! Since Heritage 2 can take HEPA bags, and has a "see through" emtor, I think it has advantages over later models (not to mention styling). "50 shades of gray" Kirby adopted with G series, makes the machines look bland, in comparison with older models. G series (in various shades of gray (with the exception of G5), looks too much like 90s (last century). Sentria has the "21st century look", but it has too much plastic on it to appeal to me. As I said, I never used Sentria, but the handle connection to the motor on the G series feels flimsy/wobbly to me. I much prefer the "pin through" handle and its positive, wobble free feel.
All that said,.....I still think that Diamond was the pinnacle of the Kirby line, although it lacks in the "looks department". The ONLY reason I voted for Diamond is the speed control switch, and if I could have that on Heritage, with HEPA bag, and the "pet hair brush", I would have my perfect "daily driver".