While I don't travel in Economy nowadays apart from 1 hour flights, all seats mentioned have extra leg room as far as I know and from previous experience travelling Economy on A330. There are disadvantages depending upon the seat, aircraft such as proximity to galley and toilets but it depends on your tolerance and duration of flight. Also preference for these seats is likely to be given to passengers with status and row 31 of A330 to people with young babies/children. Sitting near the latter may be an issue. Unless you have one of the above you may have difficulty bagging one of the seats you ask about.

If you look you may find videos on youtube.