Oxygen concentrator

[vpsdub]

Hello

2 weeks ago started to use supplemental oxygen at night, 2 liters as prescribed. Oxygen concentrator (AirSep, model VisionAire 5) tube connects to CPAP tubing. SPO2 improves to 97-98 percent with mask on, but drops back to my usual 91-92 percent when mask removed. Sleep and daytime energy a bit better.
2 issues so far are 
a) noise from concentrator, it is much louder than CPAP humming - it seems have to get used to it
 and 
b) concentrator is bulky, awkward to take on holiday trips. 

Thinking about buying portable concentrator - so far found Imogen (around 3-4 grand), Philips about half cheaper. Any experience with those? Is Imogen worth paying double? Any other good reliable brands? 

Thanks

[Sleeprider]

Many members here that use supplemental oxygen, put the machine in another room with a longer tube so they don't hear it. The portable machines can give you back your life. You can't haul a full size concentrator around.