URX4 is better. More solid, lighter and, uh, just better. Torques on ridiculously tight, like a monolithic upper. URX2-3 use alum. barrel nuts and special wrenches to install. Heavier, bulkier, more expensive and a pain in the ass to work with. You'll need a new barrel nut FWIW if you ever take it apart.
Both 11.5:
URX4, 10"? Has a Lilja Grendel bbl. and it's not a full 11.5", they include the bbl. extension as part of the length so probably closer to 10.5? Same difference, I think you'd use the same tube anyway it just fits a bit closer on this one.
URX2, 10.75", just enough room for the can to fit.
Compared to a Tavor without the can. Tavor has a 17"bbl. (this one is a 9mm). Same exact length, WAY more umph. Tavor isn't a tack driver but it is one helluva CQB and intermediate fighting rifle. And no form 1. Everybody oughta have one of these IMO.