1.) In search of the scent of Petitgrain:
In numerous citrus, green, and spicy perfumes, Petitgrain plays a role. Since it almost always participates quietly in the background, the scent of pure Petitgrain is usually inaccessible to us. So, of course, hope arises when a fragrance named "Le Petit Grain" (LPG) takes the stage.
2.) Does LPG smell exclusively of Petitgrain?
Oh dear, according to the program brochure (fragrance pyramid), many other instruments are also frolicking in the orchestra pit. How can one discern Petitgrain in that?
No panic, as perfume and Parfumo fans, we won't be easily rattled. Let's approach this calmly and analytically:
-) Can other instruments (the top notes) be detected? - No.
-) Could it be that the top notes are closely intertwined? - No, very unlikely.
-) Is there a scent development in the first 30 minutes after spraying? - No, not to a significant extent.
=> Most likely, the perfume smells almost exclusively of Petitgrain (at least during the first hour). A top note does not disappear and therefore was never present. This means the other players are just sitting quietly next to Petitgrain and watching reverently.
3.) Inflated fragrance pyramid:
It may be that a few drops of the mentioned other fragrance notes have indeed flowed in. I don't want to accuse the manufacturer of misinformation. Nevertheless, I believe that the full fragrance pyramid is meant to disguise the fact that this is a monothematic and moreover simply constructed scent. Although the fragrance name already suggests this, it seems they did not want to stand by the sparsely populated fragrance pyramid. That was fear of their own courage.
4.) Description of the scent, i.e., of Petitgrain:
Petitgrain is steam distilled from the "green stuff" of the bitter orange tree, namely from the branches, leaves, flowers, and unripe (green) fruits. And you can smell that. This means Petitgrain has a woody, dry, green, somewhat bitter, slightly citrusy scent and not at all sour, juicy, or fruity.
One could confuse Petitgrain with lemongrass or lemon tree, although it is more bitter. Among the common fragrance notes, I believe vervain (lemon verbena) has the least scent distance from Petitgrain. However, it smells more herbal, metallic, piercing, and fruity.
5.) Best fragrance from Miller Harris:
The Parfumo community has rated this fragrance as the second best among all Miller Harris fragrances, currently with 81% (from 9 votes). I largely share this assessment but would prefer to give only 75%. (Currently, "La Fumée Arabie" is rated the highest with 82% from 10 votes.)
Miller Harris has a common thread for me. All fragrances from this London house share a certain rawness, straw-like quality, dryness, and sharpness. This is not typically British.
And I don't like it either. At best, one cannot deny the fragrances an extravagant, bold style. However, the problem with less appealing, exalted fragrances is: Who wants to smell like that? It's okay for sniffing in a perfume store, but I wouldn't want to have such a scent cloud around me for hours. Consequently, I have only acquired this one Miller Harris fragrance.
6.) Use as a visual object and layering ingredient:
LPG smells quite good, but not spectacular. I hardly use it as a perfume, but mainly as a visual object for the scent of Petitgrain.
Furthermore, I can imagine using it for layering. Compositions that would benefit from a slightly woody and minimally citrus note come to mind. I spontaneously think of herbal-green and floral-fresh fragrances.
Basically, LPG could be combined with almost any fragrance. In the worst case, Petitgrain won't be bothersome, often it will simply fade into the background, and sometimes it could give the fragrance a small, elegant twist. Here lies a vast field for experimentation, enjoy!
7.) Conclusion and recommendation:
LPG smells unusual, interesting, and allows one to explore Petitgrain in almost pure form. One should definitely have smelled the fragrance.
I advise against a blind purchase, as the scent is too unappealing and (as a monotheme) not rounded enough. Whether a purchase is worthwhile or if a decant would suffice should be carefully considered.
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Addendum (on 20.01.2014):
There are also other opinions about this fragrance, stating that the listed top notes can indeed be detected.
Fragrances affect everyone differently. Perhaps my nose is not yet trained enough, or my subconscious is filtering out the green-spicy top note potpourri because it is so pleased with the Petitgrain scent impression.
In any case, after a few minutes, it should be quite clear how Petitgrain smells. Whether there is still a certain twist in LPG and how strongly this is weighted in the scent perception will be judged somewhat differently by everyone.
Top Notes 
Italian bergamot
Orange blossom water absolute
Sicilian lemon
Valencia orange
Angelica
Heart Notes 
Petitgrain absolute
Tunisian neroli
Tunisian rosemary
French lavender
Red thyme
Tarragon
Base Notes 
Haitian vetiver
Oakmoss
Patchouli
Akira1005
Rivegauche
ArneD
Yatagan
Gold
Ergoproxy
Kovex
Terra
Vrabec
Rieke2021
