I was hesitant to buy anything from HK when I first heard of them, but through the season I found out many people have had success with their batteries - and other parts, too!
So... Nowadays I run a HobbyKing 6.5T/100A sensored system - affordable at below $100/GBP62 (with customs costs I think I ended up at $120/GBP75), had the adjustability of systems that cost twice that, I haven't compared it with other sensored systems as I drove sensorless before but I am really happy with the sharper throttle response (I drive a completely different car now) and I hope I'll have a positive story on it's durability like the other drivers who use this told me
I also have two Turnigy NanoTech shorties... Half the price of the competition, the same performance it seems, and if they keep doing as well as in the long run as they do in the rest of the field here in the Netherlands, then I consider HK items the way to go for me!