The beauty of it is that due to the checksum, not all combinations are valid keys... So, you get a large number that can be discarded.
From memory, when I was brute forcing it... I didn't even know the exact letter/number for each position... So some had 2 options that needed to be checked (plus upper/lowercase for 4 options)...
Looking at
the solution post I made, my search space was 8.5 billion combinations... And I got through just over a billion in 12 hours...
My incredibly unoptimised source code is here:
https://pastebin.com/cg0TVShPAnyway, the short answer is that for a handful of keys, it's probably a viable option to brute force... Anything more than maybe 10 and you could be looking at "months" to check them all.
