Whats the differences between an UZI model A & B? Is one better than the other?

Anything a new UZI buyer should look for when selecting one?

The display barrel that comes with an UZI....is it functional....or just as implied, a display only?

Any other important things to keep in mind when UZI shopping?

Thanks.

Uzi Mod A - Open bolt, the ATF ruled that it was too easy to convert to a fully-automatic. The ATF had the importer Action ARms convert to a closed bolt mode which became Model B.

This display barrel is a solid piece of aluminum period.

Model A's are not necessarily open bolts.  I believe the first model A's imported were open bolts, but after the 1981 ruling by BATF classifying open bolt guns as machineguns, subsequent model A's were closed bolt, and all model B's are closed bolt.  The main differences between the closed bolt A and B is the sights and the size of the pin holding the trigger group on.  Model A's are more rare than B's (not as rare as open bolt Uzis which are are very few and far between).  Closed bolt model A's cost a bit more but really don't offer any significant advantages unless you've got a registered bolt.

Things to look for?  IMI Uzi's are pretty solid guns - not much to go wrong, but check the stock - it should lock up nice and tight, no wobble. Check the extractor and ejector.  

What's different about the sights between the A and B model?

The model A certainly does not fire from an open bolt.  The ATF has never allowed any semiauto that I am aware of function with an open bolt.  The model A was essentially the semi auto version of the SMG but firing from a closed bolt.  With replacement of the topcover, Bolt and drifting out the pins for the firecontrol/pistol grip assembly.. and replacing it with the SMG version. Whammo full auto.  The model A has fairly rudimentary sights that are adjustable.  The model B uses different pins for the fire control group which made them harder to replace and has an M16 style front sight and a much more positive windage adjustable rear sight.  

I currently own a registered IMI Model B Uzi and had a registered IMI Model A that I sold.
I don't know where you guys are getting your information.  I could be wrong but I'm pretty sure there were NEVER any semi-auto OPEN bolt uzi's imported in the US.  Refer to the older Uzi article in the May 1998 issue of Small Arms Review which states this as well.  
BOTH the Model A and B have a bolt blocking rail welded to the inside of receiver preventing you from just dropping in a SMG bolt.  ConfederateTexan is incorrect, you can't just drop a SMG bolt in an Uzi and change the other parts to get it to run FA.  You would have to either remove the bolt blocking rail or mill a slot in a SMG bolt.  Which either operation would be seen as creating a MG in the eyes of the ATF.
Read Bardwell's links below that detail Uzi MG configurations addressed to the ATF.
www-2.cs.cmu.edu/afs/cs/user/wbardwel/public/nfalist/atf_letter46.txt
www-2.cs.cmu.edu/afs/cs/user/wbardwel/public/nfalist/atf_letter61.txt
Shaggy, you are incorrect regarding the trigger group pin sizes.  BOTH the model A and B have the same trigger group pin hole sizes which is 9mm.  A factory Uzi SMG is 8mm.
Now back to M4's original question on the differences:
On the model A, some say that the bolt blocking rail was not welded onto the receiver as "solidly" as it is on the Model B.
The Model A has the same front and rear sights that are used on the full size Uzi SMG which are calibrated for the shorter 10" SMG barrel.  The Model B uses the newer style sights which are calibrated for the longer 16" barrel but note that they work great - just need to raise front sight up higher due to short barrel (I only use my 10" barrel since mine is a registered full auto).  Also note that IMI no longer makes the full size Uzi for their own use (some are still in service of course but they are not making new ones for themselves - I know someone that works for IMI).  But they do however still produce and deploy the MINI and Micro which both use the Model B style sites.  The Model A sights are outdated.
Another difference is that the front sling swivel on the model B rotates a full 360 degrees while the model A does not (which is like the original SMG)
The bolt assemblies are different between the A and B:
The model B has a firing pin safety which is activated by a trip which hits the ejector to allow the firing pin to go forward.  
The model A does not have this safety.  So it doesn't have this trip in its bolt and in result also using a different collar that surrounds the firing pin.
Also VERY early model A's had fully supporting rim/lip on the bottom of the bolt face.  Which would allow you to go FA with a FA trigger group installed.  Later bolts had did not have this lip.  If you notice the FACTORY FA MINI (currently IMI offers the MINI in CLOSED and OPEN bolt and the MICRO in ClOSED bolt only) and MICRO Uzi CLOSED and OPEN bolts all have this lip.  
There are some registered receiver Model A's out there that were converted this way by using these rare bolts.

Thanks for the reply fellas. Amphibian.....very informative...thank you.

Thankyou for de-bunking all the above myths. I did not know about the sling swivel I will have to check my model A SMG out.

Quoted: The ATF has never allowed any semiauto that I am aware of function with an open bolt.

I thought that several MAC style semi-auto weapons were made that used an open bolt system.  I thought they were only "banned" by the ATF from further production but the ones in service were allowed to remain in service.

Actually I am about 100% sure of this.  You can still find open bolt semi auto MACs for sale on various gun boards and auctions.

medcop

Yes, there are Open bolt macs out there that were grandfathered and I think many people confuse that fact with Uzi's.

I have no firsthand experience with Vectors semi's but I do have a couple friends with Vectors Uzi's SMG's (full and MINI's).  I have to disagree with you on them being better than IMI's.  I bought my IMI when Vectors were out and looked at many IMI's and Vectors before getting the IMI I have now.  The fit and finish of mine is superior to any Vector I have seen.  The big plus for me is that I wanted an IMI that still had the semi feed ramp so I can feed any kind of ammo in it.  At the time I got my IMI, Vector was having QC problems which they have pretty much resolved.  I have spoken to both Ralph, Rex and Robin at Vector - all stand up people and will fix any problem with their guns.  There are a lot of very good IMI conversions out there like mine but there are also a lot of not so good conversions out there.  With a Vector, you know what you are getting.  With an IMI conversion you have to know what to look for.
I also have an IMI MINI Uzi.  The receiver was heat treated and parkerized by Vector and re-engraved with SMG markings.  This is the best of both worlds.  Also Vector is still working out bugs on their MINI Uzi's since they are chopped and re-welded full size Uzi receivers.
This is not to knock Vector at all, they have a great product and service.  I am just very picky and got what I wanted in an IMI.  I also have a lathe so turning an SMG spec barrel down to fit a semi truninion is no problem for me.
Here is my IMI full size model B with my homemade Optima sight mount, the Roger Loock Grease gun mag conversion and a Craig Wheatley 50 round grease gun mag:

Here is my MINI Uzi with Gemtech Mk-9k, Docter Optics holo sight and C&S 72 round drum: