My other system has a reorder point too. Which value should I use - that, or StockTrim’s?

StockTrim’s reorder point is the optimal value. It’s automatically calculated for you based on your sales history, lead-time demand, and buffer stock. The value in your other system is usually an approximate value only, or is set manually, so StockTrim’s will be more accurate because it's based on the calculated forecasts and demand trends to be the most optimal.