We used one for travelling out of state, and used it pretty extensively here at home before convincing our DME to give us 50 foot oxygen tubes to run from the concentrator upstairs down into the living room.
We liked it - and wished we could convince the DME that they'd be more useful than a bigger concentrator and tanks. It's not any harder to transport than a tank,
The 2 key things about them are that you need to find one that does continous flow (most only do pulse flow, and the few that do continuous flow usually only go up to 3 liters, so they're not great for emergencies) and battery life.
Battery life is dependent on how much flow, so multiple batteries, and a cigarette lighter plug are a must.
Janet, crunchy pagan automotive engineer mom to Alexander, born at 27 weeks, 1 lb 7 oz | vent/trach/gtube @ 5 months for BPD | g-tube free 7/11, trach free 8/11. Also mom to Bethany born @ 28 weeks, 2 lbs | gtube @ 5 months | trach/vent @ 6 months for BPD, bronchomalacia, trach free July 2014!