It depends on how you look at it. The only downside to the whole Miele ownership are the cost of the dust bags IF you consider buying them on the high street. What you get in return is a fantastic investment with oodles of optional cost tools, even bigger than the ranges offered by SEBO.
I don't buy Miele dust bags that often from shops but rather online where I make a greater saving buying in the previous IntensiveClean dust bags that are often priced cheaper. Miele and many members keep saying "oh the HyClean is better," which is justifiable if you survive on the Super Air Clean filters alone as you get those in the pack of bags free and the extra high filtration aspect of the HyClean bags are better than the previous ones.
However, none of my machines ever use the basic Super Air Clean filters unless I want to scent my home with Greenleaf scented sachets or similar. I always buy the Active Air Clean which keeps the odours away.
Years ago now on the old Hooverland Yahoo group, someone suggested that the Miele could be used with a Hoover Telios permanent dust bag. I have not been able to find that post since, but apparently the cartridge slider can be cut to fit. I'm not sure if I would like to test the theory of a permanent fabric bag in any premium vacuum cleaner unless it is purposefully made for that model.