How old is LO? Is he drinking 25 oz in 10 hours? That sounds like too much. 25 oz would be about right for 24 hours. Are they pace feeding? Are they feeding just to settle him when he is fussy or sleepy, not actually hungry? What happens if you do less than 5oz per bottle? If he's eating every 2 hours then 2-4 oz would be more appropriate.
I agree he is being way overfed. Now that he is used to it he may protest a little of you cut back but I think you need to bc you won't be able to keep up. At that age my LO was getting more than the "recommended" amount of 1 oz per hour while I was at work (she would get 15 oz total, 5 oz bottles every 3 hours) BUT she was STTN and getting all her calories during the day. It made sense in her case that she would drink more per hour. Also I had no trouble pumping enough to keep up so that told me I was on track. You definitely don't need to supplement with formula if you were pumping anywhere close to 25 oz per day. That is enough for a whole 24 hours!!!!!
I bought these in hopes to match our other Medela 5oz bottles. The size of the 8oz is great, the shape is bigger than I thought, and the cap of bottle has problems. This set does not have the little disk's to prevent the milk spilling out. The caps are a false sense of security, as that they don't touch the top of the nipple to it thus spilling precious breast milk. If you buy this also purchase the disks to keep everything in check.