I agree that the U-Haul hitch will be fine for 600 lbs, or 1000 lbs of total trailer weight.
You can try the splice kit, as some posters have used them without problems. Others have reportedly had to take them back off, and put on the OEM module due to fault codes. I know one poster damaged his LCM, but that may have been an installation error. A splice kit is worth a try if you want to do it on the cheap.
You can always just turn off the PDC manually if you ever want to back up with the trailer.
The OEM electrical connections that come in the BMW kit are worth $200 or less (I think ECS sells them separately).
I don't know what the hitch kit costs with discounts in the US, but I assume it is something just under $500.
So yes, you can save some $$, and after all, just barely good enough to get by is probably fine. Did you use discount parts for building up your bike?
Or you could just bite the bullet and buy a real hitch. But to reiterate the first point, yes, the U-Haul hitch will tow the very light trailer you are planning to pull. Don't sweat it. Just don't ever put a heavier trailer load on it.