This falls under the, "Do I have enough capital to make the purchase?" question. And if the company fails, you get to write all this off at the previously taxed price.
Definitely a factor to consider, but not dispositive.
But be careful with this: you can write off only $3000 per year of it against ordinary income. I knew someone during the dot-com bubble who had to take a mortgage to pay his AMT from buying his options, then the stock tanked and he could only write off this $3000 a year...
