Any experience getting out of a HomeSecure contract?

As per their contract:
"Standard System Buy out fee €600 incurred in Year 1 /€400 in Year 2 / €200 in Year 3 / €000 in Year 4+"
I'm in year 5
If I stop the contract, can I keep my alarm system?
Will it still be working? What about the mobile app?

As I understand the alarm is from https://ajax.systems/
Do I need to register with them?
What about replacing parts/batteries?

Any experience on this? Thanks