I have sailed MANY MANY quantum class ship obstructed balcony cabins. I am happy with all of them. Some are more obstructed than others, but you can see the sea on all of them if you are standing. And you still get light and air on them. And the savings are TOTALLY worth it.
RC rates them either 50% obstructed or 75% obstructed. Those designations aren't precise, but they are a guide. If you call to make your reservations, or use a good TA, they have access to these descriptions.
Don't take the last one aft on Deck 6. Just don't.