こんにちは!
ご質問ありがとうございます。
ご質問について、いくつか言い方が考えられますが、例えば、
I can say this with confidence.
とすると、「これは[断言](https://eikaiwa.dmm.com/uknow/questions/81791/)できますが、(確信・自信を持って言えますが、)」となります。
例文
I can say this with confidence. I completely understand wanting to start small with a free cloud server at first, but many people eventually find it unsatisfying and want to switch to a full-featured paid service. Since moving all your data later can be a hassle, it is absolutely better to start off with an annual paid plan because it is more cost-effective, and I highly recommend it.
役に立ちそうな単語とフレーズ
say with confidence 自信を持って言う
small start 小規模スタート
paid service 有料サービス
worthwhile お得、価値がある
参考になれば幸いです。