I'm one of those people who was selling on BidStart long before it was sold to Stanley Gibbons. (In fact, I started when it was still StampWants.) So I've been following these transitions pretty carefully, because I'd still like to be able to offer individual stamps to collectors, rather than just collections and higher-value material, where
ebay has strength.
It looks like everything is migrating over from BidStart. All a seller's current listings, history, feedback, etc, is either already there or still migrating there. (They're doing it reverse-chronologically, starting with the most recent data, and moving backwards in time. I see my feedback number gradually increasing back to what it was on BidStart.)
I believe I read in their forums today that, within the next week or so, a buyer's want list and watched listings will also migrate over.
I don't know this for a fact, but, reading between the lines, it seems like BidStart's current software and servers were costing too much in time and attention to try to keep going, in addition to building a new platform as well. So, they decided to bite the bullet and get everybody over on the new sites as soon as possible.
Again, the only dog I have in this hunt is my own listings, and I'm not operating with any inside information.
I hope it succeeds, in the same way I had hoped the former incarnations would succeed, because there's a place for this kind of stamp-selling on the internet. Hopefully the third time will be the charm.