Didn’t work for us.
We had territorial marking from the existing cat. Pissed up everything. Shorted the electrics several times, blew up a telly and a toaster. Every vertical surface had piss dripping down it.
On the face of it they got along really well. Played together, snuggled up and slept together, no fighting or other signs they didn’t like each other. Just the piss.
We tried everything, for several years. Own space, own litter trays, feliway, anti anxiety medication, behaviour specialists. Cost us a fortune in vets and carpets/wallpaper/furniture.
In the end we rehomed one with a family member. Both cats so much happier, the spraying stopped. Although they had seemed to like each others company, it was obvious once they were separated that they both much preferred being alone.
Cats really aren’t that social. If they have enough to stop them getting bored- human interaction, being able to go outside, playtime- they don’t need cat company
I would never have more than one cat again.