It's SORTA better to make boomerangs, according to many people. I personally think it's not. My opinion is that it's best to make royal circlets.
Reason:Royal Circlets weigh 1 or 2 stones each. Therefore, when you set "make Max", you can make as many as 100+ per crafting attempt, before having to recycle, whereas you have to make 4 or more stops to recycle due to the weight of the boomerangs for the same number of crafting attempts. Ingots lost in recycling are the same, so it comes down to a few more attempts with less recycling breaks (once every 2-3 minutes) vs. a tiny improvement in gain chance but having to recycle every 30-60 seconds.
The lower weight also means that you can carry much more raw material on you (2 to 3 times as much) for the crafting process without resorting to pack animals, reducing trips to the bank to reload if training away from home, or reloading from a container at home.
But, yes, as you get near the end, gains slow a bit for either method (0-5 gains per 100, depending on the kindness/fickleness of the RNG).