[Sundae]

The centre that I adopted Hely from said all you can do is suck it and see. Most cats will get along to one extent or another. Different genders get along better. Two males are less likely - to the extent that even litter mates might take against eachother at 18 months.

But the overall message was positive.
They were quite happy for me to adopt a young female, knowing I had a young male in the house (both neutered/ spayed).

Unfortunately it turns out Diz is like Jehovah - he is very jealous and has righteous anger.
He will not play nice with any other cat, and only did so with Dylan because they were adopted together, from the same breeder and the same house and he faced the unknown (me!) with him.

He hated Trifle - HM's cat - and Hely, and Mia (the 'rents' cat).
But I understand he is a rarity.

Go for it, but explain your concerns to the place you are adopting from (please tell me it's a shelter!) and they will probably agree to take said kitteh back if it doesn't work out.