I have always recommended the Xintd despite not owning it. Like you say, its a well built light, good parts, screw in reflector, AR lens, Qlite and with mode options, tint options. Its a great light!
IMO L4 does have a few advantages though.
Aluminium body > brass screw in pill
Copper mcpcb which are tightly secured by screws > screw in reflector
Dual switch setup with electronic side switch > tail clicky only
Qlite vs LD-34-A. That is subjective, but the L4 is a tad more "sophisticated" (not sure if its got any sort of low voltage protection or warning yet, which I would prefer).
Buy an AR lens for the L4 and its still cheaper (depending on where you buy and what emitter option)
Looks are subjective, but id say the L4 looks way nicer. See them side by side here.
L4 is shorter.
L4 can easily be modded for higher output as well, its actually easier to add a resistor or two to it than to stack several 7135s onto a Qlite.
Im probably biased towards the L4 though, but its a reason why I bought that instead of the Xintd. So far it have lived up to my expectations.