I have the ERTL XB-35 and the Italeri rebox of the YB-49. The ERTL decals are thick, glossy, and utter crap. The Italeri decals are nicer, but matte in finish. The basic airfames are a better starting point for an awesome looking model compared to a vac-form, but the Devil is in the details, and he is obviously not anywhere near the kits! The leading edge intakes should be deep and lead to the engines, not blanked off with phony screens. The tires don't have good tread detail, the nose gear bay is too small (there is a large door that is normally closed, and opens and shuts only when the gear cycles) - ERTL only molded the well where the open gear strut door fits. There are a bunch of subtle differences in all the prototypes in the canopy, armament, and antennas. And the small details are blah looking. The cockpit captures the major features of the real thing, but again lacks fine details like instruments and proper throttle/mixture levers. (And oscillating fans!) And as others have mentioned, fit is not very good between the major parts. The problem is compounded by the fact that all the prototypes were silver/NMF. Still, they are the only injection molded kits of Jack Northrop's amazing flying wing in 1/72 scale.
Execuform had a vac-form kit with some pretty comprehensive instructions that covered the XB-35, YB-35, YB-49 and YRB-49. I've got one in the stash, so PM me if you need some information. And if anyone wants the parts to do the YRB-49, you are welcome to the parts in my kit. (Although I have no idea why anyone would want to go to the trouble of building the least attractive variant.)
What kind of suprised me is that there was absolutely no aftermarket ever made for these kits. Even Eduard never made a cockpit PE set. The kit could use internal/external PE, resin tires and "Seamless Sucker" type inlets with resin or PE vanes, vac form clear parts (the canopy configuration has several variations, and the rear blister did not always have the sighting post aperture), and a nice silkscreened decal sheet. And maybe some Quickboost resin propellers, as cleaning up the spinner collars is a pain.
Sorry, that's a lot of negative whining on my part, but the XB-35/YB-49 sereis of aircraft were among my favorite aircraft. But if you just take your time and build it OOTB and get a decent silver/NMF finish, it will look stunning.