First, I have read other reviews that state to not tighten the grip bolt and the barrel. I disagree - do not OVER-tighten them. Snug is good. Anything else will loosen up on you, and will disappoint you after spending the money that you have on both the Neos pistol and the carbine kit. Additionally, if you are not able to fasten it properly, then there is something wrong with either your pistol, carbine kit, or you are making an error somewhere with how you have put it together.
When I first received the kit, it unfortunately was defective. The slot for the magazine catch in the grip was machined (or cast-?) too high. When I would fasten the grip onto the receiver, none of my three (spectacular) Beretta factory magazines would load properly. Hence, it was entirely useless. I called Beretta, they told me that no one has ever called on this type of problem before. I returned it for a full refund (no shipping cost to me in either direction), and purchased a new one. Thankfully, the new Neos carbine kit worked as intended.
The performance of the working carbine kit really surprised me. Zeroing the sights, my groups were within a centimeter at 7 yards (again, this was to zero the sights). The Tru-Glo front sight works as it is designed to do: it takes the ambient light that is available, and quite literally causes the sight to appear to glow (a fiber-optic design), with no batteries. To date, I have only used the stock Tru-Glo sight up to 25 yards, so I do not know how easy it is or is not to use beyond that, but it sure makes for a great time shooting bulls eye targets when I used it.
Assembly/disassembly is so easy that a child could do it. Just make sure to lock the slide back (after safety-check of course) before you begin, or springs will potentially fly out and get lost.
As other reviewers have stated, the stock is pretty short, but it did not bother me.
And recoil - what recoil? If you have shot the Neos pistol, you know that the recoil is minimal at best - very easy to shoot. When shooting the Neos with the carbine kit, there was literally no recoil to speak of. I know that a lot of you will say, "well, yeah - it's a 22 long" - still, I was very impressed. I know that my 5' tall 110 lb. wife will have no problem shooting it (once I can convince her to come with me to the range!).
The weight is light - very manageable.
For ammo, I used several types, and the Neos Carbine kit shot all of them - not a single misfire, even with the cheap stuff. I used Winchester 555 bulk JHP, Federal 550 bulk JHP, CCI Blazer LRN (el cheap-o), CCI Stinger JHP, Remington Target LRN, and CCI Standard Velocity LRN - it ate EVERYTHING, with no "reflux"!
This item loses one star not because of performance, but because I found that the molding looked kind of cheap at the seams down the middle of the butt/stock. As a personal preference, I am in love with the "futuristic" design, but after spending a lot of money on the pistol, the carbine kit, an extra magazine, and the 5 colored sight pack for the Neos, I could not help but be disappointed with the seam. Also, considering that for the price of the carbine kit, I could have bought a complete rifle of another brand, I do wish Beretta included some sort of carrying case for the kit. Not that I would want to pay more for it (note to Beretta - don't add a carrying case to please us and then raise the price), but even the simplest canvas case would have been nice.
But as I state above, the performance of this gun is excellent, fun, cheap to shoot (22LR, of course). I am thrilled with the purchase of this kit; a fantastic addition to the pistol, that is well worth the price. FOUR WELL DESERVED STARS.