I don't know that you can make a really strong argument to buy one as a "must have"...there isn't a think that it does that can't be handled as well or better by other guns.
BUT...and that's a big "but", it does a couple of things really well. First, it's a great plinking/range gun. Ammo (9mm at least) is cheaper than .17HMR so you can have a ton of fun with it at the range. It's a good truck gun; not too pretty that you couldn't toss it in the back of your truck and bounce down a gravel road. the calibre is small enough that you can shoot gophers without blowing them to pieces, but still has enough punch to knock down a coyote or a beaver with no trouble.
It's also made me re-think a home defence gun. Like lots of others, I have a 12 ga. that will get business done...if I'm shooting it. My wife is not crazy about it because of the brutal recoil, so it may as well be a single shot instead of a semi auto; she's not going to pull the trigger a second time. The JR, really in any calibre, but 9mm especially, has almost no recoil. At 10-15 ft. she can tear through a full magazine and keep a group you can cover your hand with in around 2 seconds. No huge concern with over penetration, even with hot FMJ rounds.
I never expected that this gun would get nearly as much use as it does. My copy has worked flawlessly; dirty, clean, factory loads, hand-loads, FMJ or cast bullets...doesn't matter, it eats everything. I have had one FTF in 1500 rounds...one. That one round had a bad primer. It's a very solidly built, nicely machined rifle. I REALLY like the concept of it being ambidextrous and being able to change calibre's without buying a new gun. So much of it is AR compatible, you can tweak it as much as you want.
Do you NEED a pistol calibre carbine? Damn straight you do! Buy one. Shoot it lots. Smile.
