I gave up my 12 bores about 4 years ago in favour of the 20 bore and haven't looked back. I shoot and o/u Beretta and use it for duck flighting, rough shooting, pigeon decoying,driven game and clays.
I love the light weight of the gun and the fact I can shoot 24/28/30 gm cartridges as the mood takes me. It is a great gun for snapshooting but harder for crossers until you get used to it (lack of weight/inertia)
The only downside, as mentioned above, is the rip off cartidge cost.
Cheers
Sib