I'm not sure what functionality the 308 has over the 106, but I'm going to assume they are basically the same firmware, and mainly offer different charge rates.

I have a 106 and do most of my charging at home before racing, then just top-up at the track (this is 2s only). For my needs this is great, and I have a couple batts per vehicle, so I don't need the fast rate of 30A (I don't even charge at 10A).

If you are in to planes or heli (or plan to), then the 30x series would be what you want.

I personally would get a decent charger (not overboard) that fits my needs, a spend the remainder on a good radio.