As this comes as a duo, it's hard to have both as outstanding. Each brush has one end that I really like while the other end is not really my favourite.
To me, the thickness and length of the bristle is very important. Some other eye brushes have either too thin bristle or the length is not enough. The shade end of the brush is great but the define end doesn't work well for me. The define end is an angled eyeliner brush. It's very thick and difficult to use, especially when ur newbie to eyeliner or you want to create a sharp and precise line. The blend & smudge brush is quite nice. The blend side is soft and easy to use but I prefer the smudge end. The smudge end is really a highlight to me as it's dense and thick. This is my go-to brush when creating a smoky look.
I got this little set of iherb.com and I am pretty happy with them.
First off the double ended nature of these brushes presents the same problem as the urban decay double ended brushes included with all the naked palettes, that is...How do you store the little devils? I ended up just storing them all in my normal brush holder with the least fluffy/more dense side down and they don't seem to be suffering.
The brushes themselves I quite like. The Define & Shade brush has an eyebrow brush on one end which I find really handy (as I don't have any other eyebrow brush at the moment) and fills in my brows nicely and on the other end is a reasonably sized flattish shader brush which I use for packing colour on the lid and also to blend shades into the crease. The Blend & Smudge brush is just as useful with a small dense blending brush on one end (which is actually a little to dense for soft blending) and a short flat smudge brush perfect for smudging eye shadow along the lash line.
For the price I think these are a great buy, they aren't the most amazing brushes on the market but they are soft, don't shed and do a pretty good job at an everyday makeup look.