Yen Chee Design review for Mailchimp Email SMS Marketing

I used this app to sync Mailchimp with Shopify. It was the only FREE option that I had. I would love to have Klayvio but it's more than I wanted to pay at the moment. I read the warnings of how emails were sent to old subscribers, but I had an even more strange thing happen. I had an additional 179 people imported into my mailchimp-emails that were never even on my subscriber or unsubscribe list, and totally unfamiliar to me. Has anyone else had that happen? I have no clue where these random emails came from, but suddenly they received my automated "thank you for subscribing" message and then I had to delete each person individually which wasted hours of time. For some reason mailchimp was not letting me delete multiples at a time. I don't know why this would happen, and now each time I delete a bunch of foreign emails they seem to keep getting added back in. I'm terrified to even use my mailchimp to send a mass email because I'm not sure who's going to get it. I'm tempted to bite the bullet and switch over to Klayvio.