Good thread. Let me offer a bit of info on the feature. It is free you just pay commission when it sells.
We added this a couple years ago as customers requested it, here is my 2 cents on the option. It is a good feature but there are many listing types and you need to try and find the right one for you as all names and all sales are not created equal. The advice I am offering below is general, there will always be exceptions to anything. I am just trying to lay out some high level things to consider.
If you have a great domain say a 3L.com you are going to get offers every day. These types of domains are probably best left unpriced, possibly with a floor price ( a minimum offer price) to weed out the bad inquiries and then take the offers and negotiate the best price you can on an individual basis. Don't price these names and don't put them into an auction. A small percentage of names fit into this general category.
If you have a good name say a great two word .com or 2L .net or something that is getting consistent offers every month then you should either think of the price you would want for the domain and BIN price it (higher than you want) with an option for offers or keep it at offers only. Again there are probably not tons of names in your portfolio getting multiple offers every month.
If you have a name that is brandable or two good words you are probably best off with a BIN price on the name and listing it on Afternic. You may lose some money on an individual sale here and there but you should more than make that money up by selling more names overall. BIN priced names sell on average 3x of offer names. So in the long run pricing the names is the best sales strategy we have seen on these kinds of names. These are names that might get a solid offer every year or once every couple of years.
If you have to list with offer only even after reading the above, then you should really consider strongly whether pushing to auction makes sense. Here's why, if your name was already getting a lot of offers regularly then you would probably be less inclined to throw it on the auction you would just sit back and wait for the right offer to come in that was higher. If it is not getting a lot of regular offers then what's the likelihood that all of a sudden this name is going to get a lot of offers all in one week in the form of bids? Slim to none.
People like to buy a name when they are excited about it. The longer you drag out the process the less excited people become, you need to strike when the iron is hot to close a deal. If someone comes in with an offer that is not what you want, in my opinion it is better to tell them right away and try and negotiate higher while they are excited about it. Presumably you are already fine with accepting the initial offer because you know pushing the domain to auction means you are bound to accept the winning bid anyway, i.e. the initial offer if there are no other bids. So you have an interested buyer and they want your domain and it is unlikely you will drive the price up by placing it in a week long auction if you are not getting regular interest in the domain anyway so why not either just accept the offer and get the money or negotiate higher before people lose interest?
Now push to auction does make sense in some situations. Let's say you had a domain for 5 years and haven't been really interested in selling it at say $5k but now you need money for something and $5k interests you. If you have had offers over the years that you have declined but still have a way to contact them, or you think you can draw more eyeballs on the domain by posting here or advertising on blogs etc then that makes sense. If you think you can get more bids by contacting interested parties and you think you can keep the excitement going by creating a bidding war then this option is the right one for you.
Sorry for the lengthy response, but I get this question many times so hopefully it can help some other people as well. I hope you sell your domain for a great price.