Both of them are able to fulfill your requirement, Netflix is mobile version, which is exclusive membership;
Without updating firmware, the rest of apps will be available for updating to latest version;
3pro and 3S diff:
1) 3Pro is jailbroken set with Google playstore, and Shafa UI (remove xiaomi original interface and AD apps). The most import feature is bypass china restriction, If you have Kougou or some VIP membership, it’s more convenience;
2) 3S, on the other hand, is unblock set, with Googel playstor, and Android TV UI. The most import feature is it support 4K Youtube, and running latest version 6.0 instead of 3Pro is 5.0.