I'd say the Sigelei 100w + is worth the extra $20 or so. Shop around, you should be able to find it under $80.
What worries me about the Arrow is the cheap battery tray, fixed 510 connection and the usb charging port--I doubt that at $60 they have a balancer on board and charging 2 batteries w/out one is risky.
If you go with the Sig, pick up some fresh batteries and "marry" them so that they remain balanced.