Hi Jon
I think a 9mm AR is a good weapon for home defense and range practice (especailly if there are no rifle ranges near you). If you have a weapon, you should be completely familiar with it and well practiced with it. In putting a 9mm AR together, you will learn a great deal and 9mm is about the cheapest ammo you can buy for real range practice.
As for 9mm in an AR: unless you have a professional need for 233/5.56, I would venture to say that 9mm in an AR is a fine choice. You cannot use .223 for hunting in some states and for home defense, 9mm is a perfectly fine, in a carbine. If there are no rifle ranges near you, you can practice with a 9mm carbine at many pistol ranges. Not trying to start an argument here, just my opinion.
And...if you practice using an AR shooting .22LR, you will not be practicing for defending yourself using 5.56. With a 9mm AR, what you shoot at the range will be what you shoot defending yourself. Just my opinion.
Not sure about some of your choices above. One choice does not list what magwell block they are selling you. Would not do that. The magwell block is the single most important part of a 9mm AR build. If it is not a good one, your gun will never be reliable.
There are two ways to go. 1) Buy a dedicated 9mm AR from a maker, or 2) put together a 9mm AR, using a standard 223/5.56 lower. IMO, putting one together is the way to go.
If you buy a dedicated 9mm AR, it can be 100% reliable and function well. You can get ones that use Glock mags. But...they are expensive and that is all that gun will ever be, 9mm. To me, this obviates the reason to have an AR. But, it is not a bad way to go to get a gun that is 100%.
If you put together your own AR, you have an AR. Since you will have a standard lower, you can put on any upper you want, including many that are excellent for hunting ...and defense. 6.5, 6.8, .300 and the 7.62x39 (AK) rounds might be better to have than 223/5.56, for some applications. SO, with a 9mm AR, you could have a great HD gun, great range gun, and with the addition of another upper, a very good hunting gun. That is versatility.
In order to put together a 9mm AR, this is all you need:
1. A standard AR lower (223/5.56 or multi-caliber). Maybe $250.
2. 9mm buffer ($25)
3. Magwell block ($50-200). This is critical. It is how you use 9mm magazines and get the round into the chamber. It is critical to the reliablity of the gun. SO....get the very best you can. The cheap $50 plastic ones are not good. IMO, get the Spikes or Hahn dedicated. I have a Hahn dedicated and it has been 100%.
4. Colt type 9mm magazines. (get good ones: Metalform, C Products, Colt)
5. A 9mm AR upper that ...most important...can be used with any standard lower. I have the CMMG. it is very good, reliable and not expensive ($500-600). It comes with a ramped bolt and is ready to go when put on a lower, as configured above.
That is it. Once you understand what parts are needed, it is simple. Really, it is a standard lower with a 9mm buffer and magwell block. Then a 9mm upper that can be used on any lower.
One note: it is very tough to do this inexpensively, you will have to budget $1050-1100. You CAN get a decent 223/5.56 AR for $600. And a .22 adapter for $100-200.
Hope this helps
Best
John