The smallest common clarinet
The E flat clarinet is the smallest of the standard clarinets, about a third shorter than the B flat- or A-clarinets. It is noted in E flat, which gives it its name. The notes are noted in the violine key and fingering is the same as on a B flat clarinet - except that everything is a bit narrower.
Most e flat clarinets produce a sharp, sometimes shrill sound. In symphonic works the instrument is usually set - because of its tone range - unisono with flutes and oboes (which often means wild acrobatics in extreme hights) and it is often not easy to be exactly in tune with an E flat clarinet. Especially not unisono with flutes - when warming up they show different behavior concerning tuning than clarinets, so you must frequently re-tune.
Quite often - and generally in amateur bands - a "normal" clarinet player does play the E flat clarinet in addition to playing a first clarinet; and more often than not that will be a simpler, that is: less expensive instrument (since the industry produces less E flat clarinets than B flat clarinets the instrument is rather more expensive).
Combined with the challenges both in technical and intonational problems this is a very difficult task. In my symphonic wind band the E flat player is usually the one clarinet player with the best "ears" and excellent technical abilities.
Tough on your lips - and how to cope with it
The considerably smaller and narrower mouthpiece and reed presses harder on the lower lip than that of the B flat clarinet. In order to prevent biting into the lower lip, many E flat clarinet players put a piece of thin leather over the lower jaw.
Short keys - but nothing for kids or beginners
This instrument is a challenge for people who already play even the most technically challenging parts with ease, and have got excellent hearing - maybe a good alternative to becoming the first clarinet player in an existing orchestra. This instrument is not a kid's clarinet and not suitable for a beginner! Kids should better wait until their hands are big enough for a B flat instrument.