I have had great luck with turnigy and zippy. All of my turnigy packs have come perfectly balanced and I have not had one failure. The nano techs are great and have been performing well for me, although I have only used the stick packs. I did try a gens ace once and did not feel as much rip or runtime. The pack came with one cell at about 3.4 and the other was at 3.83 so it could have just been a faulty cell.

Front Slipper Pad:
When running not pinned i.e. decoupled with the VTS slipper, the VTS is only controlling the back wheels while the single slipper pad on the back side of the spur controls the front. Since the VTS has more grip due to the design, you end up wearing out the front slipper pads. When I installed my VTS I put a new HD pad on as well (on the backside of slipper). When I disassembled the other day I noticed that the VTS pads looked new and the pad on the back side of the slipper was wasted. This means that although I was running the overdrive front end, the slipper pad was so worn that it wasn't really 'pulling' from the front rather just letting the fronts keep up with the back. Also under power or braking, the front slipped and the rear gripped (slipper pads, not tires), making the truck act more like a 2wd. It actually works good for a tacky tight indoor track but really bad on a loose outdoor.

IMO: If you are running the VTS slipper uncoupled with the overdrive front end I would check/replace the front slipper pad regularly. Coupled doesn't matter as the VTS slipper is used for both the front and the back.