I was attracted to the product both because of its price and the rave reviews.
First the science bit:
St Moritz has both a developer tan (the chemical dihydroxyacetone, known as'DHA') which takes a few hours to deepen, and an instant tan from its coloured dyes (Red 40, Yellow 5 and Blue 1).
The best comparison is like when you go for a spray tan, which has strong coloured dyes as well as a tan that takes longer to develop and lasts about 5-6 days. However, unlike spray-tans St Moritz lacks the more expensive chemical Erythrulose which takes 6+ hours to develop and is included in most spray tans (though NOT in most off-the-shelf tan lotions).
In terms of results, well the colour upon application is pretty convincing, as others have noted. However, I had a lot of difficulty getting a truly even result, and would not recommend using this on the face as you can be left looking very 'dirty', with mild marks and changes in colouration looking particularly obvious. It works better on areas that are less 'fussy' to apply like the legs, back and stomach.
My biggest problem with both the Dark and Regular St Moritz, and the reason I don't consider it a credible sunless-tanning option, is that the 'intant tan' dyes keep leaching out of the skin even after you've showered it off. This is despite using fairly coarse exfoliating gloves and giving the skin a good scrub all over to get them out.
So everytime I sleep or sweat even lightly (which let's face it is quite a lot in summer, especially if you go to the gym or do any kind of exercise) my clothes and bedding become marked with reddish-brown stains which are very difficult to wash out and leave everything a slightly pink colour once washed.
On top of this, there's the fact that while waiting for it to 'set' (4-6 hours), you essentially can't do *anything*, as even brushing up against the wall or sitting on a chair leaves a surprising amount of colour stain behind. And after then you really must shower or else everything you touch will be stained. And after showering you still need to wear loose dark clothing and do your best to avoid sweating, getting wet, splashing your arms or face with water etc. It's a real pain and massive limitation compared to other tans that don't have such strong instant tan dyes.
So as good as the St Moritz colour may be, I don't feel it's worth all the hassle that comes with the instant tan component staining everything and making it very difficult to actually get out and show off your new tan.