I bought and use mine strictly as an assistant. I dont use it to track exercise at all. I love not having to take my phone out of my pocket every time I get a text. I use Cortana to reply which is seamless. I do also use it to track my sleep however it needs to get better at identifying restful vs light sleep. All in all I'm very happy with my purchase.
This appears to be correct. All apps actually run on the phone. The Band just kicks them off and receives data. There are more apps appearing every day for the Band. My current favorite is Band Camera Control which allows you to take a picture with the Band using a voice command through Cortana. Also check out Band Sensor Monitor. Well worth $1.50.As of right now, I don't believe apps can "run" on the band, and they may never... The SDK is just for sending notifications to the band and syncing fitness info from the band to the phone.
We'll have to wait and see if a future SDK opened it up for more, but there are no guarantees.
I think it's alright to use it solely as a watch. It might feel a bit weird due to its shape where if you wear the face facing above your wrist,you'll have to read the watch in a slightly awkward position but it's fine if the watch is facing down. Also on the lowest brightness setting,it is still readable under the sun light. The only disadvantage is that it is not fully waterproof (maybe just splashproof) like most normal watches so keep that it mind.
Received mine today and have activated Watch mode. How much of a hit will I take on the battery life?