Had similar experience when we bought an older house. Its expensive either way, but I think it'll be cheaper with the metal. They just manoeuvre the flexipipe down the chimney and backfill the space between it and the original structure with concrete. It's a much simpler procedure, but if you need to compare, just ask for a quote for both, but you can simply imagine the extra work involved in dismantling brick/block work and then rebuilding, compared to the above. Good luck! Ours has worked fine ever since by the way.