Posting on ProductHunt, if you're a small company, can be harmful. Program Managers of big companies prowl this site, looking for interesting ideas to copy.
Timing matters. A big company can snuff out a small competitor if they respond quickly, before the small competitor gets a chance to take root. Once it takes root it is harder to snuff out. So it makes sense to stay out of sight of big competitors until you have had a chance to establish.