I've heard mixed reviews. I've been debating joining one too. Some people only get sales from the BNS and that's it, others it increases their exposure so much that sales continue. If you only do one I would think that you'd only get a few sales. Do one every other week and yeah, sales will probably stay steady.
I think it's more about your level of commitment than anything else. If you can guarantee that your shop will always have a few items in it and always have something new (especially if you do it every other week...if the same people are participating they might get tired of showing the same products and having to choose from the same options) than maybe doing a few would be a good idea. If you think that it would be tiresome to constantly keep up on top of that, especially just starting out, or that you'd end up spending more than you'd be earning than maybe it's best to wait.
