Naruko am+pm Total Brightening Renewal Treatment 5% Mandelic Acid

Pricing/Packaging:

30ml (1.05fl.oz) for ~25-37$ (naruko usa). This serum comes in a cute opaque white glass bottle (have to admit, I was really drawn to the packaging). Product dispenses through an easily controlled glass pipette. As most Naruko products, it should be used up within 6 months after opening.  

Ingredients:

Water, Hyaluronic Acid, Butylene Glycol, Mandelic Acid,  Gluconolactone, Tranexamic Acid, Propanediol, Arginine, Sodium Lactate, Niacinamide, Panthenol, Lactic Acid, Sclerotium Gum, Glycyrrhiza Glabra (Licorice) Root Extract, Essential Oils of Lavender, Eucalyptus, Marjoram, Thyme, Clary Sage, Rosemary, Ho Wood, Methylisothiazolinone.

Excellent (only beneficial ingredients, proven research)

Good (mostly beneficial, not extensive research or just not quite outstanding properties)

OK (mostly thickeners, emulsifiers, mild preservatives, pH adjusters, all that is necessary, but not a skincare per se) 
Bad (irritants and anything bad that shouldn't be in a skincare, usually fragrance)

Ingredients Discussion:

I have mixed feelings about this serum. On the one hand, the first two thirds of the ingredient list are amazing, but on the other hand, the last third is quite bad.
This is a brightening complex, that promises to eliminate dark spots and improve overall skin tone, which it really can do, due to the presence of niacinamide, tranexamic acid and licorice extract (all known as pigment melanin suppressors), as well as mandelic acid. Mandelic acid is lesser researched alpha hydroxy acid (also known as amygdalic acid). Some research shows it to be as effective as glycolic acid, however there are definitely a lot of gaps in stability and safety data. It seems to be very sensitive to the UV exposure (though the packaging in this case is quite opaque). Additionally, lactic acid and gluconolactone present in here will offer some exfoliation as well. It seems that this product is also formulated at a correct pH (3-4), to allow those acids to actually work. Overall just from exfoliation and three mentioned above melanin suppressing actives, you should have skin brightening and lightening results.
This formulation also features high concentration of hyaluronic acid, as well as panthenol, both of which hold on to moisture in the skin and improve skin barrier function. Additionally, arginine and licorice extract in here have antioxidant and anti-inflammatory properties. Lastly, niacinamide does not only work as a melanin suppressor, but also as a cell-communicating ingredient ("sends" cells message to work like healthy skin cells).
All of these ingredients make this serum very potent and quite well rounded with all skin essential components. Unfortunately, there are 7 essential oils present. Luckily they are at the bottom of the ingredient list, but they still are able to inflict irritation upon the skin, which can "undo" positive changes coming to life due to the presence of good ingredients.

Consumer Thoughts:

This is light, watery, but quite hydrating at the same time serum. The product has medium/light hebal medicinal scent, which didn't bother me too much, but wasn't my favourite either.
Personally I didn't see improvements in brighteness of the skin or changes in hyper-pigmentation spots. But my skin is quite accustomes to array of similar products, so by now it is hard to see any results when introducing new product.
It is definitely a noteworthy product. But I will suggest to be very careful, if you have known reaction to fragrance or essential oils or have sensitive skin. It would be neither my first choice for skin lightening treatment, nor a long-term use product. 

Verdict:

Undecided. I can't recommend it wholeheartedly, but at the same time this product has some potential. Not a long term use treatment (since long term exposure to irritants can cause low grade skin inflammation), but worth of trying out.

3,5 out of 5.