Double strike and Haste have good chemistry. I can see them together for a long time. Would you rather have this then paying more for a 2/2 or 3/3? A 1/1 is awesome really early game, and gets so much less impressive after turns 3-4. This card could benefit then from a different creature type, one supported by Lords (like Goblin) for instance. Or it would be extremely fun in a set with a lot of exciting Equipment or Auras.
The P/T are definitely scalable. A 2/2 for 2RR should be manageable at uncommon, and I could see a 3/3 for 4RR or 6R at the same rarity. I designed this card for a set where devils are the main black and red creature type, so it would be supported in the format it's available in.