Oumo Element/ST-2
My random thoughts on Oumo synthetics (photo below):
The ST-2 knotted brush left 'completes' my Oumo synthetic collection (all 27mm).
Can't go wrong with any of these knots, they all work very well but they do have different characteristics (what follows is obviously subjective):
From left to right, softest to stiffest knots: ST-2, ST-1, S-1 Sparrow, ST-1 Extra Dense.
The ultra-soft ST-2 (bulb) reminds me of my wife's make-up brushes but the lather-making is as good as the other knots, if not better. If you can get past the powder brush feel, it could be The One. Oumo recommends a lower loft setting. Some tout the ST-2 as Oumo's answer to Wald's synthetic - but I've never tried a Wald. Maybe someone who has both could comment?
At the other end, I'd recommend the very stiff ST-1 Extra Dense (fan) for those who mash 'n bash their brushes or like a lot of scrub.
The ST-1 (bulb) and grey Sparrow (fan) are the most conventional: the Sparrow is the slightly stiffer of the two and a lot cheaper but I've read reports of prominent glue bumps especially in the smaller Sparrow sizes and/or bulbs (no bump on my large fan Sparrow or indeed any of the other knots).
So I'd perhaps recommend the 'all-rounder' ST-1 if you're starting an Oumo synthetic collection. It's an excellent knot and reminds me of my first generation Mühle STF, perhaps slightly stiffer.
If you're making your own handle for an Oumo knot, Oumo handles have a hole about 20mm-deep. If you like to set your own knots (as I do) and also order an Oumo handle, make sure to specify this through the site chat function or they'll set the knot for you by default. Mine are Oumo handles and I added a plastic washer (about 2mm) to all four brushes which suits me with the knots I chose (I don't like short lofts) but of course we all have different preferences.
My four Oumo handle models (left to right): Element, Big Hand, Venus and Fortress - all at the lower end of Oumo's price range and acquired during Oumo's frequent discount sales.