I used Sendgrid as part of a RocketChat install in 2021, and the deliverability was atrocious. I vowed to never use it again, but haven’t explored alternatives recently. What options are you looking at?
Since the application for Dittofeed is similar to Mailchimp, which would be newsletters mostly and not transactional email, is that compatible with your primary business case at Resend? From what I can tell, Resend is mostly focused on transactional email and not on mass email messages such as newsletters, which is what I see as what Dittofeed is sharing with their Mailchimp alternative. If you're open to newsletters, let me know, and I'll give it a switch from Sendgrid!