user...202, it depends on what you'd like from a Vit C. The facetheory one uses Sodium Ascorbyl Phosphate as their stabilised Vit C, it has its benefits but in comparison to L-Ascorbic Acid and second choice MAP there is very little research. The research that is available suggests it may do the brightening and pigmentation tasks like AA on the supposition that it converts to that but the emphasis is on may. So if pigmentation and brightening is what you'd want it for it wouldn't be my first choice, although FT have put in some licorice root extract in the serum to cover that somewhat. As for aiding in collagen production it performs weaker than MAP which is already less than L-AA (so as an anti-ager it isn't of much interest in that sense, it does have the UV protection boosting properties like other Vit C forms so in that sense it is of interest anti-ageing wise, albeit slightly more one-dimensionally).
What it is good for is acne, some studies suggesting it is as, or more, effective than benzyl peroxide without all the side effects, so as an antimicrobial acne fighter that's also an antioxidant it looks great on paper. The Mad Hippie Vit C Serum, which is quite popular on the Skincare Addiction Reddit, also uses SAP so it does have its fans (but I suspect it is of the acne suffering sort as that mostly populates that Reddit). That one is around 10% SAP and I do wonder if there is any benefit to a 20% version as SAP has better penetration abilities than L-AA (one of the major drawbacks and why the low pH/high % combo is needed) so a lower concentration would be just as good (the studies were all in the 1-5% range). The Mad Hippie is about twice the price though so in that sense the FT becomes interesting. I wouldn't take the offer price too seriously, everything is always discounted to the same prices on there along with the discount codes. Side note, if you do want to buy it I'd contact FT first and ask about the pH, SAP works best at a pH of 6-7 which would mean you also wouldn't use it in the traditional place before BHA and AHA post cleansing like with L-AA but instead after both BHA and AHA.
eversions, how are you using the CosRx (don't remember discussing this product introduction previously, last I remember the PC BHA gel and other acid left you tepid, hence the prepping toner talk)? It's always sensible to build up use no matter how gentle they're supposed to be, so 1-2x a week to start. I also only ever recommend introducing one product at a time, I sort of assume that even if people can't read all the threads back they've at least read through most of the current one so I don't need to continually repeat the basics that cover this, leaving plenty of time to evaluate a product before introducing the next one, not washing your face in the shower, etc.
PHA work a lot like AHAs but are of a larger molecular weight meaning they have less of the sensitising side effects of AHAs. But since you're experiencing issues with the CosRX currently hold off on these for a bit, please.
JDSTER, yes P50 is considered a strong acid (iirc between 9-12% and lowish pH) but much like PHA, lactic acid has a larger molecular weight and is therefore less sensitising than glycolic. I'm not against them as a rule (peels I do find a territory like derma needling where it's sensible to wonder how easy access should be), just feel they need to be approached with caution and a certain amount of guidance.
I think you should start with 1-2x a week for the Retinoid (I'm assuming the 2%, yes?) You can do BHA in the same routine but I'd avoid it (initially) if you can).
yongnian, ten-year-old me is giddy with excitement over the pony! What are the colour options?
SashaTaught, I'll take a closer look tomorrow if that's okay. I don't know what platform you're using but on desktop and mobile browsers there's a choose file option underneath the message box to attach files, alternatively, you can PM me and you can email the pics if you prefer.
Kennington, true, acids will be acids and IME formulations are everything when it comes to them and this is the one skincare realm where I've found spending a bit more reaps better rewards, though I'd happily be proved wrong by TO. However, these formulations carry a lot of similarities if you place the INCIs side by side. I've put them in a google doc here to avoid clogging up the thread. Direct copies they are not (and possibly we're just disagreeing on the semantics of it) but dupes doesn't seem to cover it for me but possibly is the correct term.
I did notice the 2% Salicylic is presented as a spot treatment so I assume it'll be a little thicker texture wise and fits in on their low use acid philosophy slightly better that way, encouraging topical use. INCI wise they added witch hazel which is a shame as some people are quite reactive to that and it lacks the soothing extracts of PC's formulation.
The 7% Glycolic is very similar to Pixi as it has that glycolic-aloe-ginseng-glucose formulation, TO using rose water instead of fragrance to give it a bit of scent. It's not exactly the same, but it feels far too similar, I did read today that Pixi is highly priced in North America, around $40, which kicks it firmly outside of the affordable realm there so I guess it's fair game in that sense. I've never been a big Pixi fan due to some of the irritants (that the TO version doesn't have, though rose water is irritating to some) so this actually looks to be promising for those in need of a daily 'gentler' AHA toner.
The peel is based off Drunk Elephant's T.L.C. Sukari Babyfacial which is a 25% Glycolic TLC + 2% Salicylic peel/weekly treatment. The TLC (Tartaric Lactic and Citric) acid combo with glycolic really is a DE signature. TO is definitely a simpler version of it but again, they look very similar.
I did just have a very traitorous thought about using the peel on my KP arms after all the side eyeing of it these past 24hrs
Meh, Dulci, I continually mess up Azelaic, Salicylic, Matrixyl and countless others 
I had the same thing with the Niacinamide 10% thought it was true love and that we'd never be parted but it stopped being impressive after a while and my routine didn't suffer at all without it. Was very weird that way.