I don't know anything about the Sebo brand or how they function, I can only speak for the kirby. Now as for the Kirby they haven't changed much, especially over the past 30 years. I feel like growing up using a kirby was ok, but it had its issues, as with all kirbys and Im going to list them and state why this is an issue.
(1). The noise
These machines are extremely loud and unbareable to tollerate, especially when using it on hard surface floors. There where times when I rather have just used a broom and sweep than to turn on that machine, because of how loud it was on hard surface floors.
(2). Disengaging the belt
This ties in to the first issue. When having to use the kirby for floors, You'd have to disengage the belt and then use it to clean the floor. This was to time consuming and the belt, which was always in good shape, would always smell like burning rubber.
(3). Storage
Storing the system wasn't that big of an issue. The issue I saw was when storing a bag that has dirt and junk, your storing a breathing ground for bacteria and all that stuff.
Now onto the issues with the accessories and attachments
(4). The Shampoo system
The system was a nice concept and has improved somewhat over the years but can use a major overhaul. The system to to big and bulky looking when attach to the main unit. How do you explain to clean hard to reach areas with it? The same can be said with the updated MS3 system, that allows you to clean all flooring type surfaces. Not mention its too loud. The issue that kirby needs to fix with its shampooers is scaling down the overall size of it, so it can hit in harder to reach areas.
(5). The zipbrush.
This is a nice accessory but it needs improvement. One thing I didn't like about it was that the hair and dirt would get stuck on the brush and not sucked up into the main unit. I think Kirby needs to change that to where it does get suck into the main unit when using it. Also kirby should make it motor driven and not air driven that way it has more power to it.
Those are some of the things I think kirby needs to improve in future models. Going from a kirby, growing up, to now using a dyson cordless for day to day cleaning, I can say that the dyson is a lot quieter and more manuerable than a kirby and it saves on time. The same can be said about my Rainbow SRX. Its a lot quieter and more manuerable than a kirby. The accessories and attachments are also easier to attach and use than a kirby.