Is iRobot A Good Investment?

I bought iRobot at $30s and sold about half of the shares hold at over $100. I regret that I failed to sell them all. Even after iRobot's dropping about 40% from the top, I am still hesitating whether to go back into the game with more investment because I am not sure whether the company can defend their leading position in the long term. It seems that many companies can make a robotic vacuum cleaner now.

Here is an excerpt from a brilliant article that Warren Buffett penned in Fortune in November 1999, "Mr. Buffett on the Stock Market:

All told, there appear to have been at least 2,000 car makes [operating at one time or another in the U.S.], in an industry that had an incredible impact on people's lives. If you had foreseen in the early days of cars how this industry would develop, you would have said, "Here is the road to riches." So what did we progress to by the 1990s? After corporate carnage that never let up, we came down to three U.S. car companies--themselves no lollapaloozas for investors. So here is an industry that had an enormous impact on America--and also an enormous impact, though not the anticipated one, on investors.

I won't dwell on other glamorous businesses that dramatically changed our lives but concurrently failed to deliver rewards to U.S. investors: the manufacture of radios and televisions, for example. But I will draw a lesson from these businesses: The key to investing is not assessing how much an industry is going to affect society, or how much it will grow, but rather determining the competitive advantage of any given company and, above all, the durability of that advantage. The products or services that have wide, sustainable moats around them are the ones that deliver rewards to investors.

With iRobot's shares' PE over 30, the risk is high even in the short term.