I found a really good deal on SB600 that is 1 year old and the guy says he used it only once. He is about 45 minutes away from where I live. Price is $150. Please advise how good of a deal this is. Also I wanted to purchase SB700 but for the price savings what will I not get in SB600 that SB700 has to offer. I've never used a speedlight before and I am not sure how much/how often I will use it. Thank you!