No experience of the X-RF4 four speed hub. AFAIK, this hub is aimed mainly at small-wheel bikes, for a normal-wheel bike you would need a rather small chainring to get a reasonable gear range, and small chainrings wear fast.
I did consider the X-RF4 for use on a Brompton a few years ago, but I ended up using old Sturmey-Archer S5/2 hubs manufactured in the early 1980's instead - the S5/2 is very slightly heavier than the X-RF4, with 5 gears instead of 4, closer gear steps and slightly more range. And in my experience very reliable, I have done over 100,000 kms with S5/2 hubs. I still have 3 of them in service, but they have become rare now.
More recent Sturmey-Archer "small" 5-speed hubs (Sprinter, 5-Star) were less robust than the S5/2 and had reliability problems, but I don't know how the "large" RX-RF5 does in this respect.
If you can manage with just 3 speeds, an old Sturmey-Archer AW3 can usually be found fairly cheaply on Ebay, the last one I got was about £20. In my experience, the AW3 is very robust and will keep going for decades. Weight is similar to the X-RF4.
For use on large-wheel utility bikes I am very satisfied with the Shimano Nexus 8 in the "Premium" versions, I currently have six of these in service on various family bikes.
The Nexus 8 Premium is about the same weight as the Shimano Alfine 11, quoted weight (probably without the fittings and gear shifter) is 1685g.
Direct drive on all the Shimano 8 speeds is gear 5, so IMO they are more suitable for large wheel bikes than the Sturmey 8 and 4 speeds, which have direct drive in the lowest gear.
The latest iteration of the Nexus 8 Premium is the Shimano Nexus SG-C6061 range, these have better-quality internals than those in the entry-level 6011 range, so the hub is claimed to be more efficient. In practice, I don't really notice the difference between Nexus 8 Premium and Rohloff for local riding. The Rohloff has much more range, so is good for very hilly areas.
The jumps between gears on the Shimano Nexus 8 are closer than those on the X-RF4 and AW3, which suits me better. Overall range is 307%, which is enough for local utility riding in my area.
Externally the difference between the entry-level 6011 and the premium 6061 is that the latter is labelled with a blue line on the hub shell. Alfine 8 is more expensive and has a better finish on the hub shell, but the internals are very similar to the 6061.
If you choose a Shimano Nexus 8, be careful about the version. The DI2 version is often offered for sale at a low price (SJS currently have them on sale at £99), but you need the expensive electronic shifting gubbins because the DI2 will not work with mechanical shifters.
Shimano hubs for mechanical shifters are often sold without the fittings - gear shifter, cable, sprocket, and "cassette", the latter is the essential kit of parts that transmit the cable movement to the rotary gear change on the hub itself.
