he is getting between 91.5% and 92.5% reduction.
The website does say the average result was 93% @ 750 GPD, so he isn't miles away.
H is going to get over 16,500 Liters from a sack of DI Resin, so that itself is costing him half a penny per liter. If he uses 200 Liters a day, 5 days a week, he would still only need to refil a 7Ltr resin bottle every month. If he uses 100 liters a day for 4 days a week, then it would last him two months between refils.
My point is, that although 30 is higher than most of us would like, at 92% reduction it is working and it is doing what you want... cutting the costs. We can easily slip into the mistake of thinking the RO is for bringing our TDS down. It isn't! Thats a shock eh? The RO (or merlin) is so we can produce pure water in a cheaper way.