I personally wouldn't buy the 50w charger. That is very limiting to what you can charge and at what amperage rates. You best bet is to get one or two of the 400w chargers as you can charge many lipos these days at rates of 5c and higher. get a 200w x 2 charger f you need. Heck, get a PL8 and parallel charge.
I got one of the sky rc 400w x 2 duo chargers and can charge a pile of batteries in no time at all.