Please also get a urinalysis after a month on his special diet to monitor his crystal levels.
Just as a different perspective, my cat Jake had a blockage due to struvite crystals. He was prescribed Royal Canin SO wet and dry. I was told he was high risk but a urinarlysis was never suggested nor performed by my vet to confirm his risk. Due to its high carb content combined with Jake’s weight issues, after 3 months I ultimately decided to switch him to low carb all wet with extra water.