I was a member for one year and didn't feel it was worth it. You can get the same info from WebFlyer and other travel sites for free.
I think the deal with the TWA fares was that Carl Icahn, in his deal to get out of TWA, received a couple million worth of tickets. He is selling these via Best Fares, thus the TWA connection.
The only good piece of advice I got from Best Fares was to joint the Delta Airlines Women's Connection. You can join even if you're a man and you do get one coupon for a one-way upgrade (between certain dates) and a couple of car coupons on National. I used my National coupon last month at LAX and got the car for free for 3 days--just had to pay the taxes. You can join via Delta's website.