Overall it sounds like a good opportunity in my opinion. If you've been at your current position for a while, then you don't need to worry as much about 'baseline' experience. If the offered job went under in 6 months, you'd still have the baseline experience and should be able to find something else fairly easily. If you've only been in the industry for 6 months or something - I'd stick around until until you've got 2 years as that seems to be the magic 'baseline' experience for basic work - or at very least 1.5 years and assuming you'd have a job for 6 months.
If you aren't sure your own company would be anymore viable than the newer one - then it's best to just discount it as a factor in your decision.