I have had it for 1.5 years with 5 to 7 hours of daily use and it presented a problem, all the alarms that indicate multiple problems went off. I contacted the seller of the product via email and they responded that I need to send it for service, which I will do and I will update on the progress of the issue.
Unacceptable for it to have problems in 1.5 years, before this I had a rented machine for 5 years and it worked perfectly.

And the inconvenience continues!!!

Email to the seller
On Friday 10/09, I received the oxygen concentrator after 40 plus days. I inform you that apparently no repair was done, nor of course any testing to verify its proper functioning, because the concentrator continues to have a problem, the oxygen alarm goes off 10-15 minutes after it is turned on.
After the above, I strongly complain about the irresponsibility that characterizes the service of the concentrator. I inform you that the cost of shipping has cost me 70 euros (Kalamata Athens Patra Athens Kalamata) and I am not willing to incur additional expenses. Please let the person responsible for this inconvenience bear the costs.
This week I will send you the concentrator for your actions.
Note that the machine is under warranty!
17-01-22
I received the machine in late October and until now in January, it has been functioning without any problem except for a noise that it didn't have before, although it is not very annoying.