Yamaha Saluto is a durable bike as it comes with the peace of mind of being a Yamaha. You seems to be a great fan of 125 cc motorcycles and have gone through every aspect of the bike clearly. Its good to see you so happy with your ride and I would suggest you to go for a normal checkup at a Yamaha service center and as them about the power of the disc brake. Being a 245 mm unit, it definitely would be lesser powerful than 267 mm units on most of the bikes but would be definitely 2 ties better than a normal drum brake. You have paid a premium of INR 2,500 for the disc brake and you should ask them if there is any problem with the same.