you can't sell the shares.
Not quite true. Look at pg 29 of the prospectus (
https://6303ffd34a16b1ca5276-a9447b...3.rackcdn.com/BrewDog_EFPIV_Prospectus_UK.pdf), 4. Trading Platform. You can sell shares on Asset Match once a year. Good luck making a profit, though. In fact, the last time I read further into this the shares were trading at the list price but after the 3% trading fee as a seller (in addition to another 3% as a buyer!) you're probably looking at a loss.
I looked into this a while back. In summary: Don't. If you want the warm fuzzy feeling of helping a company out (remembering that they are, after all, a company intent on making profit, not to be your best friend) then go for it but don't consider this an investment for a moment. If you want to make a beer-related investment 'just because it's your interest' there are certainly better options out there... But of course the better the investment is, the more likely the company are to be a huge business making beer for money, not passion. I think I'd keep my interests and my investments separate...
I was going to write some more but I think the following search from a quick Google does a much better job:
http://themissingdrink.com/investing-in-brewdog/
BrewDog make good, perhaps not great, beer. If there's one thing they're even better at, though, it's marketing (have a read of Business for Punks by BrewDog co-found James Watt). If you really want to give them some money then just buy the beer and drink it!
EDIT:
I only bought a pair of shares at the time but its saved me a fair bit so far with all the discounts.
Based on the above article (I've not double checked the maths) in order to make back your pair of shares you'll have to spend ~£1000 at BrewDog. Unless you've managed that already then you've not 'saved' a penny (you're still out of pocket!). And, if you have spent that sort of money on beer since making your investment, added to the fact you've chosen to invest to begin with, you must be pretty interested in beer - In which case a grand can buy the avid beer drinker a much more diverse range of beers than sticking with, and only with, BrewDog!