If you are considering investing keep in mind that Berkshire is trading at 1.5 price-to-book ratio. Is there an actual reason to buy the stock instead of roughly replicating their portfolio and maybe periodically rebalancing? You might get slightly different returns but you are not paying a massive 50% premium + fees.
Also Buffet and Munger are in their 90s and I am not sure how the stock will react when the inevitable happens. Personally I would stay away