OK, so I'm trying to decide for a range toy.  I've never held or shot an AR pistol or .223 pistol, and I already have a carbine.  

It seems like the Extar ($450) and a bottom-of-line true AR pistol build (~$600) are my current interests.

What I want:
Range toy for fun
"Big boom"
Smiles for me and other range guests

What I'm not interested in for such a purchase:
Home defense
Sling use
Suppression (minimum barrel length)
Getting into arguments about pistol stock usage

The Extar EXP-556: (less so with PLR-16, other .223 non-ARs)
I like:
Lightweight
AR-15 controls (as opposed to PLR-16)
Magazine compatibility
Some part compatibility
Sights come with it

I'm not sure about:
Longevity
Warranty
Non-standard parts compatibility

An AR pistol build:
I like:
AR-15 controls that match carbine
Magazine compatibility
Full part compatibility
Build-into-rifle or other caliber later

I'm not sure about:
Weight (Are they really 6 lbs?)
Reliability challenges -- finding the combo of buffer and gassing that works

Can anyone offer some opinions either way?

if you just want a toy man buy the toy/range gun extar fits IMO what you want ,

I built my 5.56 strictly as a range toy. Same general criteria as you. Loud, plenty of muzzle blast and smiles.  I only shoot it at my indoor range and it turns heads every time. As far a lower muzzle velocity out of the 7.5 barrel I don't care. Not shooting anything more than paper.

I bought an Extar when they first came out--my serial is 150-something. I ended up converting it to a more standard AR pistol with a Sig brace. Here's why:

Out of the box, the thing was horribly over-gassed. Empties would eject over 30 feet from the gun. Fired cases were noticeably bulged around the back end, and one of them actually ripped in half (which caused a major jam because the front half stayed in the chamber). The over-gassing was compounded by a lighter-than-standard bolt carrier, and no buffer at all. So the action was unlocking when there was still a lot of pressure in the chamber, which was causing the bulged and separated cases.

Also, the handguard on the Extar has no ventilation whatsoever, so heat buildup is a problem. Especially given that a lot of the gun is polymer.

I bought a Blackthorne polymer upper, full-auto bolt carrier, Syrac Ordnance adjustable gas block, and a lightweight Midwest Industries ventilated quad rail handguard. I also bought a pistol buffer tube and Sig brace. I used the original barrel and bolt, and rebuilt the upper so I could adjust the gas. I threaded the lower and drilled a hole for the buffer retainer pin, then installed the buffer tube and Sig brace. I also replaced the original muzzle device with a Noveske KX-3 "flaming pig".

With a standard carbine buffer, I was still getting slightly bulged cases, even after adjusting the gas so it was only 2 clicks above the minimum setting needed to lock the bolt back. I ended up using an H3 buffer to slow the bolt down a bit to give chamber pressure some extra time to drop before the bolt unlocked.

After the rebuild and gas adjustment, it's a smooth shooter, empties only eject about 8-10 feet and are not noticeably bulged, muzzle flash and blast are fairly reasonable, and with a FastFire III red dot sight, it will shoot 3-5" groups at 100 yards. It's still pretty lightweight, controllable during rapid fire, and a lot of fun to dump mags with. Last time I shot it, I dumped a Beta C-mag full of Wolf through it and it handled it just fine.

I'm happy with the thing now, but I'd have spent considerably less money if I'd have built it right in the first place. The Extar is an interesting idea, but as designed, it doesn't really work chambered for 5.56.

Now if it was chambered in 300BLK, the lighter-than-standard bolt carrier wouldn't be an issue because 300BLK pressure drops off faster than 5.56, and premature unlock wouldn't be a problem. Now there's an idea for a new build project...

I have an Extar and love it !!!  
If you want a range toy, and a real attention getter, this pistol is for you.
I have put aver 600 rounds through it, without a hiccup. I cleaned it after 300 rounds, and then again after 600 rounds, and I see NO evidence of any abnormal wear at all.
Accurate, LIGHT!! and no recoil.
The Extar pistol sells out quickly, so get one when you can, it is also made entirely in the USA.
If you go to YouTube, there a ton of reviews for this pistol, and they are overwhelmingly positive.

Have you tried rechambering a fired case? Will it go in all the way? Does it stick in the chamber? Mine wouldn't go in more than halfway, and would get stuck enough I had to punch them out with a cleaning rod .

anyone else?

Haha, love when people mention turning heads, or purposely having loud brakes, etc. Just like the South Park episode with the Harely owners. Making loud noises with they weren't on their bikes to get attention. "They think we're badasses."

Pistol AR is fun. About the buffer weight, don't worry about it. Use a standard one and if it doesn't work, return it. If it's a build, get a heavier one, based on how over gassed it is.

Something I'd think wouldn't be fun about the Extar... I didn't enjoy my M-85 PAP (5.56 AK pistol) last time at the range because I knew I wasn't controlling it very well. Felt like shit, so an AR pistol with even just a standard buffer tube to shoulder or at least get a cheek weld, almost required. Idk, that's my two cents.

Does anyone know if the Extar takes standard AR15 Barrels?

Would be neat to add a pinned 14.5 inch, a polymer lower along with an AGP folding stock to keep it light weight yet compact.

Yes. Some caveats:

The upper is not standard. Besides the obvious side charger and action spring enclosed under the rail, the barrel nut threads are larger than standard. That means that you cannot use any handguard other than the one supplied with the gun, because the barrel nut WILL NOT fit. Also, the rail on the upper is 5/8" higher than on a standard AR, so using BUIS with the front sight mounted on a standard rail is impossible unless you can find a 5/8" tall riser.

You cannot use a standard upper on an Extar, unless you convert the lower to accept a standard buffer tube. Extar does not sell uppers separately.

The Extar also uses a non-standard gas length that's roughly halfway between pistol and carbine. If you change barrels, you'll need a new gas block and gas tube.

Got ya, actually I've been thinking.

This in 300 black out might not be bad at all for a truck gun.

I considered an Extar but they didn't look as badass as a decked out AR pistol

I have both and enjoy both.  

The Extar is the party animal of the two...incredibly light, no recoil, very loud, and seems reliable so far.  It works better with a tight two point, one just above the grip over the shoulder, and one at the front of the handguard running under the opposite arm.

The AR pistol is going the SBR route with two uppers, one in 5.56, the other in 6.8.  Forked over the $200 just this week.