After testing a whole stack of these macarons I can confirm that the break rate does hit rock bottom but at the cost of less HQs even after testing it out on a T3 synth. Based on 641 total synths I only failed 14 times which is roughly 2.18% fail rate, which is improved drastically basing it on a 5% rate, the downwards is I only got 113 HQs (doesn't matter which tier since its the same) which turns into 17.62%, comparing it on a rough 50% based on a T3 synth.
This makes me believe that a really good use for these is synths that don't require HQs and whatever loss costs a lot of money IE Imp. Wootz ingots.
For those wanting to know how i tested it, I synthed Meat Mithkabobs (cap 38) with a cooking skill of 100+3.
The Kitron Macaron is one of a family of foods which have similar descriptive text ("Preferred snack of artisans", "Beloved dessert of artisans") and apparently no visible stat bonuses of any sort:
Tested this out while skilling-up Alchemy (and working on Smithing/Goldsmithing subs) from 10~56.
From 10~50 skill, break rate was VERY low. Typically skilled-up using a gap of 3~4 from skill to cap. Skill-up rate appeared to be about 1 skill-up every 2 synths on average.
Also of note, desynthesis fail rate seemed to be significantly reduced as well.
After level 50, the bonus to skill-ups seemed to drop off entirely, but the break rate was still very low.
If/when I return to crafting, I'll try to remember to keep a detailed log of synthesis results while using this food and update.