The glossary is very, very useful for a translator. In general, there's a paid version, but the free version is quite good.
The translations tend to be very, very accurate. So, those are the main pros. You do really notice the quality of the work. You can't trust it 100% because you're not giving it enough context sometimes.
But in general, you can trust that it will always do an okay translation.
In terms of cons, the fact that you can't really personalize it that much or give it as much input. So you can choose between a formal and an informal tone, but that's it. You don't have as many options for a tone or the sort of translation you want done.
If I'm thinking of more professional translation tools because DeepL is kind of in the middle. Like, it's for an everyday user. It can also be used via a translator.
But if I compare it with more professional translation tools, it doesn't have a few features like the options of storing more specific sentences or storing certain fragments and comparing the original text with the translation and just making subtle changes, that you can store in memory to then use again in a different document.