As a seller, I have tried bidstart numerous times, going back to its original launch as stampwants. I ran items in parallel with
ebay on several occasions. It never was even remotely close. My sellthrough rate at bidstart was a tiny, tiny fraction of that achieved on
ebay.
As a specialty buyer, it's even worse. I purchase on
ebay weekly. Bidstart and stamps2go, maybe once every 6 months. Delcampe, a complete and utter waste of my time: if it's not fake, it's overpriced.
Believe it or not, the online venue I purchase from the second most frequently behind
ebay, and while a distant second it is still worthwhile: the APS online stamp store.