Should I roll for Cu Alter ?

Well, that's up to you. I'll roll for him because I like the character and because I don't have many single target servants, especially berserkers, so he'll solve two of my problems if I got him.

go for JAlter if you have heracles

Heracles is a solid enough Berserker that you don't really need any other single target choice.

If you like Cu Alter enough though, then go ahead.

If you have him with bond 10 or plan to bond 10 him, skip

If you like him, yes.

If you feel like heracles is enough, no.

Cu alter and Heracles play differently as well.

Cu Alter does very well if there is a team that can help him survive and make his cooldowns shorter as well as taking attention away from him so his 2-hit evade works to its full potential, while Herc does best as a last-man clutch, with on-demand evade, guts and valor to increase chance of victory with damage+.