I am currently using an M6 tank and getting ready to get a new system (POC). My question is as an experienced 02 user, would you recommended a unit you carry or push? I am finding carrying the M6 tank around is kind of a pain and gets heavy. I use an E tank at home that I push but not sure how convenient it will be outside. I am prescribed for exertion but finding myself using it a lot being once I get up my level drops. So think I will have to get something large enough to handle 2-3 lpm and last 4-6 hours. Any help or suggestions you have would be appreciated.