Just bought a CZ Canvasback that I'm going to duck hunt with this year and was wondering if I should get some extended chokes? What purpose do they serve?

I would shoot the gun with your waterfowl loads with the chokes you have and pattern the gun. Just like you would a rifle. If you are happy with the patterns at 30-40 yards buy more shells, if you are not buy chokes.

I personally like LM in the barrel I am shooting first and IM in the second. Not sure about CZ Chokes but Carlson's Chokes are what I normally buy. Briley's is also a well respected choke manufacture.

Good luck and shoot them in the face...

Carlson's or Trulock's

Remember, shooting steel shot use a more open choke than with lead shot.

x3 on the Carlson's. I have extended chokes on several and my wife's o/u has extended chokes that are ported, pretty noticeable difference in recoil with those!

If its for the duck and goose blinds, I wouldn't recommend ported chokes, your hunting buddies won't be buddies for long with the excess noise and muzzle blast. Like stated above, try the factory chokes first to see how they pattern. I get real nice pattern from my factory chokes on my duck gun, so there is no reason to switch. I did so however on my favorite upland gun, and the results were much better overall. Using Briley Lt Mod and Lt Full in the O/U.

I like extended chokes so I can see at a glance which choke is installed. They also protect the crown. I use Trulock and Carlson's.

I like a Kicks choke. But what was said up top, pattern the chokes you have now as you may like them! Hopefully you find something you like!