I was a first time brewer (cider, actually) and decided to take a chance on the conical fermenter. I had troubles with the first 2 batches, in that there were no bubbles in the airlock, although the cider itself was fine. I purchased a 2nd o-ring and, after several variations, got a good seal on my 3rd batch by using the provided o-ring with the new o-ring (and quite a bit of sanding/cutting of the fermenter top to be sure it was smooth). Problem solved.
I went to bottle the 3rd batch and had a complete valve failure during the ball and bottling tube exchange (seating gasket on the top slipped, which allowed cider to flow past the valve). Bottling was not much fun with this batch.
I e-mailed the company and their customer service was great. Jes asked some questions and mailed me a new valve assembly. My 4th batch was flawless (from a brewing & bottling point of view). No leaks, no mess, no problems; good seal at the top. I was very happy.
Ultimately, I've grown to really like this product - especially compared to my brother's method of fermenting cider and wine, which requires the transfer stage. With the 4th batch, it really was as easy and clean as they say in the ads.
If you are considering using this product, I strongly suggest trimming and sanding the 6" opening on top to ensure a good, air-tight seal. Also, be generous with the plumbers tape provided. I've never had a liquid leak (except the valve failure). If you do have issues, give the company a call or e-mail (they actually tried to call me back a couple of times) and give them a chance to fix the problem. I suspect they will be able and willing to help out.