Hi Patty, I have one of the little portable concentrators. It works well for my purposes, but there are some limitations which may not work for everyone.
It weighs around five pounds, plus maybe another half-pound for the extra battery, which does not store on the device. The version I have only goes to 3 liters. Carrying around 5.5 lbs plus an extra battery in your purse can get heavy, but hasn't been a problem.
Both batteries give it about a 3-4-hour life, and less at higher liters. The main reason I use mine is travel in the car, and it has an adapter. You can use it while it's charging, which is a blessing. It works all day. For short trips, like to the doctor, it is also useful, where I am able to connect to their supply if there is a wait. At my daughter's house, I can plug in the transformer to house current and breathe easy forever. The batteries have an LED battery-charge indicator, which is handy, and they hold a charge for months. (But check in time to charge both, if you have two, to make sure). I leave mine plugged in by the back door so it's always ready.
I have taken it shopping, which seems to work well, but only for short trips, no window-shopping strolls.
So, for my purposes it works fine. I don't need high liters, and there are machines which do have that. I think the key is knowing what it will and won't do, and arranging around the limitations.
I rent my unit from the oxygen carrier, and In our area, it is now impossible to get a second battery. I was provided one originally, but, they appear to be in high demand. My Medicare Advantage plan pays all but about $20 per month, but this can vary with the plan.
Hope this helps.