The Petzl Tibloc is one of the lightest and most compact ascending devices out there. It does a great job grabbing icy ropes and is very compact and lightweight. It does not replace a tradition handled ascender]. Instead, it's meant more for emergencies.
If you have the money, this is a great device. If you are on a budget, and mostly a rock climber, I would probably just use a prusik cord instead. However, if you are a mountaineer and want a device that will grab icy ropes in an emergency, this is a great device. If you are looking for a real full-function ascender, check out the Petzl Ascension Ascender.