I like that they're able solve any issue you have with sending bulk email! They've got it all covered for me; my only complaint is having some difficulties when using templates in Gmail as opposed emails end up being blacklisted by Google so those types don't work at times either - but nothing too bad about this service overall (just one thing).
And best part? It's super easy & fast customer support team!! Have used them multiple time now since 2015/16 without an instance where their services were not perfect enough!