● It's easy to lose track of time when you're on the Internet, so you have to be careful. You really have to try it to understand (why), but it's more addctive than you might think. ● You have to be careful when you're logged on to the Internet. It's easy to lose track of the time. You'll never really understand until you try it, but it can be (more) addictive (than you imagine).
addictiveは「中毒性の」の意味。これを使ってit's more addictive than you might thinkで「思ったよりはまる」と言っているのです。
These muffins aren't bad. Not bad at all. 「このマフィン悪くないじゃない。いけるじゃない」。