Westone is in the business of making audio equipment, and more specifically in the case of earphones, making a series of devices known as in ear monitors or IEMs. In essence, it is one of the leaders in earphone branding, right beside Shure, UE and Sennheiser.
It generally falls in the slot of the high range earphones with prices from 100 + and up all the way into the few hundreds and even to thousand. It also has multiple drivers, which you will see in the name. For example the westone um2 has 2 drivers.
While it faces stiff competition, westone has more than held its own in the high end audiophile market against those other companies mentioned earlier. It sticks to a few of its best products and carefully hones them. It doesn't bother with "not so good" build quality to output cheaper designs that won't last as long and have lousier sound like say Creative or Sony Walkman. Instead, it has two main lines, that of custom fit and then universal fit, and even then its only separated into one for occupational use (professional musicians) and one for personal enjoyment (active lifestyles). It also has a rather long warranty period.
Instead westone focuses on durable and professional quality equipment, making sure that its armature driver provides a powerful and dynamic sound that will cover a good range. It also only have IEMs, but are very customizable, with about 10 different kinds of ear tips available for most of its designs. You can swap between those with higher noise isolating power or noise reducing power, or those with a better bass tip (westone comply tips tend to cut off bass, but the true fits modify that for mass market tastes) and stuff like that. Of course you would have to buy them separately. It also makes it easier to clean your earphones, as you can buy replacement ear buds once they've gotten rather dirty.
Common praises of westone earphone products is that their In Ears at the universal fit actually does a remarkable job of staying in your ears, even if you are out running or doing vigorous exercises. It can be considered a "perfect fit" for most people. Another praise is the value of its earphones, where each driver is pegged to a price that is value for money, even if it would be expensive to those who are not so "into" music. It easily holds its own against say Shure with strong price competition. Another thing is that even its entry level earphones, like the UM1 have exceptional engineering, and sounds wonderful in sound balance and reproduction.