I would not look at the Kel-Tec RFB as an alternative to the TAVOR. They are like apples and oranges. As much as I like and want a RFB, I would have it as an additional .308 weapon, not a alternative to something else. To me, the TAVOR is one of the most innovative and robust weapons ever made.
I like my Tavor. A lot. That said, it has some obvious shortcomings and only two really standout features going for it.
The good:
It's short. Really, really short. With a full 16" barrel. This translates into better ballistics than my 11.5" AR with shorter overall length.
It's balanced so you can very comfortably maneuver, aim, and fire it with one hand. I can do it with an AR, but it requires more effort and concentration.
The less good:
It's not as accurate as my ARs. Out to 100 yards the difference is pretty minimal when shooting offhand. At 300 it's pretty noticeable. I mostly attribute this to the aforementioned balance. There's no weight out front to keep things steady. It's also not real easy for me to shoot prone, though I'm sure more time with the gun might reduce that particular problem.
Definitely not as easy as an AR to switch strong/weak side on the fly. It can be shot on the off side, but it takes a bit of care to not get your face in the way of the workings. Again, more time with the gun might reduce that problem as well.
The trigger is atrocious, and the current aftermarket options are some combination of completely unreliable, very expensive, and/or not yet available. Hopefully this will change soon
The BUIS, while niftily integrated and included with the rifle, take up a lot of rail space. I don't consider this to be a huge deal, as it's not a gun really suited for a magnified optic, but I'd rather have no rail where the BUIS sit instead of rail space that's unusable without mounting the accessory over the folded sights.
Overall I'm very glad I have, and greatly enjoy shooting it. Were I stuck with only it to defend myself, I wouldn't feel at all unarmed. That said, for most uses, I'd rather one of my ARs.