You can't calculate it because it depends on the daily movements. Start with 100, one day is +25% and the next -20%. Index is still 100, but SPXU went +75% and -60% which brings it to 70. If the 2 days are flat, then SPXU would be worth 100.
No you won't. It provides exposure to the daily returns of the index. That means in some cases over the course of more than one day it will return more than 3x the inverse and some periods less, it's entirely dependent on the path the S&P takes. It's not a "tracking error" unless you fail to understand what it's tracking, which is 3x the inverse of the daily again that's DAILY return. It actually has very little tracking error in doing exactly that. If you think it should be returning 3x the inverse of the S&P 500 returns over a week/month/year then you simply failed to read or comprehend the prospectus, that's not a "tracking error".
So it's no good as a hedge in a 2 or 3 year bear market? Then only thing left to do, other than taking a cash position, is shorting SPY etf in a IRA account as a hedge to 401k. Thoughts?
Not that I know of. A couple of obscure ones track monthly returns, I wanna say in the MLP space? If you find any though let me know, I last researched this about a year ago so things very well could have changed.
Of course it's good as a hedge in 2-3 year bear market. But due to costs of leverage, your "3x hedge" may become "2.8x".... or even less if you've held it long enough.