The D2 is a fairly accurate device at higher wattages where it doesn't have to buck below battery voltage. And it always had a functional resistance lock, it just displayed realtime/last fired resistance.
For $40, it's hard to beat the combination of size, light weight, solid Yihi chip, and power output potential. For what you're looking for as an on-the-go beater device, I think it's hard to justify spending an extra $100+ for a DNA200.
As for the Velocity, it's a great RDA, clone or otherwise, and it'll spoil you to the point where you won't want to go back to "primitive" center post build decks like the one found on the Goblin.
@Two_Bears, the Joyetech eVic VTC Mini is also a solid choice in that category and price range, though it's physically taller than the D2 and lower wattage (60w), it makes up for it with that excellent display, better build quality, standard USB connector, firmware upgrades, and the bypass mode is a nice feature for somebody coming off a mechanical (which also makes up for the lower wattage in regulated mode).