This is a great offer to get your cat fixed and microchipped. Depending on your area, desexing a cat can cost over $200 (especially for female cats).
As others in the comments have mentioned, please remember that pets are for life – oldest cat lived up to 38 years old! I took in two cats who were born in a barn and they've been a wonderful addition to my family and I wouldn't trade them for anything in the world.
Regarding eligibility, I gave them a call and it sounded like the eligibility is dependant on whether they have a partner vet that can service you in your area or close by.
From the Cat Protection Society website:
FOR A LIMITED TIME ONLY
Book in by March 10 to get your new forever friend:
🐾 desexed & vaccinated
🐾 microchipped & registered
ALL FOR $50
Please call us on 02 9557 4818 (Monday to Friday, 10am to 5pm) to see if you’re eligible and get in quick to take advantage of this ameowzing offer!
Remember - a pet is for life. Not for Easter.