Since I haven't used Samsung Galaxy J3 Prime yet so hard to say real life performance of it but Xiaomi Redmi 4A seems far better option in my opinion. I am using this phone and it has good performance, strong battery backup, good cameras. I am satisfied with its features at such a low price. Samsung Galaxy J3 Prime vs Xiaomi Redmi 4A
Coolpad Mega 3 is better phone than Samsung Galaxy J3. It has more RAM , better cameras and bigger battery than Samsung Galaxy J3 Prime but samsung has better after sales service and cheaper than Coolpad Mega 3. Samsung Galaxy J3 Prime vs Coolpad Mega 3
Samsung Galaxy J3 Prime is not available in India yet. Samsung phones generally has good build quality. There should not be any problem . However, from specs I feel that 1.5GB RAM is less in today's world and cameras are just 5MP and 2MP.