Question about Braun Series 9

I only clean the device when I have to charge it. Currently, with the new battery, this is the case about every 14 days. o Considered, the cartridges last a long time. I also clean them after use, let them dry and refill them with a much cheaper replacement product from the internet. Works flawlessly for years.
Opinions differ as to whether this device is the best Braun. In any case, the much more expensive "Plus" shaving head is useless. Fortunately, the shaving heads of the series 9 also fit. What has bothered me with every Braun shaver so far is that the shaving head fixation is too weak. If you press a little harder, the shaving head disengages or moves one position further.

After about 2 months, they have to be changed. I shave every three days. So I would estimate about 20 applications.

I haven't even used this cartridge yet. I rinse the shaver with water. That's enough. Maybe I will open the cartridge after 6 months.
By the way, this Braun is the best shaver I have ever had.