Hi, how old is your baby? how long have you been expressing for and is your baby currently drinking any of the ebm?
I returned to work when my dd was 3 mths, but i was parttime and flexi hours. Since she was four weeks i started expressing and dp would give one bottle a day to get her used to the bottle.
I too often only got 2 or 3 oz at a time, i'd bag it up and freeze straight away and then get two or three bags out to defrost per feed required in bottle. Before i returned to work, i used to express as often as poss, i would bf baby on one side, then put her on the other boob and express more from the first boob whilst she still fed. I found this easiest as she had 'started' the flow making it easier. I also seemed to get more out if i expressed whilst sitting in a warm bath.
Whilst i was at work, i always left emergency cartons of formula in case ebm ran out. By the time dd was 6mths she had had a couple of these cartons and i was exhausted with expressing so decided to start giving her all formula whilst i was away and then bf when i was with her. This worked fine for me, and i continued breastfeeding her until she was two. I was lucky enough to be able to plan my working day so i had time to come home at least every six hours and feed dd as there was nowhere suitable for me to sit and express to relieve my boobs. If you're working full time and not able to do this then you will probably still want to express anyway whilst at work.
Whatever you choose to do, by 6mths your supply is unlikely to dry up if you're still bfeeding morning and night.
Sorry if this is waffly! In answer to your actual question, no i havn't tried that pump, but i think it is normal to only get 2 or 3 oz's, as your baby gets older you may find you get more out and you will be surprised how much you end up collecting in your freezer.