I'm setting up three sites for a customer. Three sites or a multi-site?

I'm not really sure what to choose here. I have little to none experience with multisite but I'm thinking this time should be a good try. Is there any cons to using a multisite instead of three single sites?

The customer has a brand and want two subsites (on their own domains, I guess I'll use the Domain mapping plugin for this). Any takes?

Thank you