The Respironics Evergo is a good portable oxygen concentrator. It has a weight of only 8.5 pounds and operates for 4 hours on the battery at setting 2. However, it comes with only a 2 year warranty and only provides pulse oxygen dose.

The Invacare Solo 2 has a three year warranty and provides almost twice the pulse oxygen dose as well as 3 LPM continuous flow. However, it only last 2.6 hours on the battery at setting 2 and weighs over twice the amount of the Evergo.

The Sequal Eclipse 3 also provides a 3 LPM continuous oxygen flow and has a 3 hour battery life at setting 2.

If higher doses of oxygen are necessary, the Invacare Solo 2 or the Sequal Eclipse 3 are better choices. If weight is the primary concern, then the Evergo or the Invacare XPO2 (weighing a pound less than the Evergo and with a 5 year warranty) are both excellent choices.

A detailed review of portable oxygen concentrators can be viewed at the bottom of the following web page.
http://www.vitalitymedical.com/Catalog/Portable-Oxygen-Concentrators-1162-.html