These are two different kinds of products.

I assume the portfolio of TEGBX remains relatively stable month-to-month. The portfolio of GIM changes frequently. Thus GIM, a more risky investment, commands a higher yield.

Also, as a mutual fund, TEGBX always sells at its net asset value (NAV), but GIM, an ETF, trades on the exchange for whatever price the greed or fear of daily traders invents. During market dips in 2008 and earlier this year, the day traders panicked and GIM traded substantially below NAV for long periods of time - sometimes as much as a 25% discount - something that couldn’t happen to a mutual fund.

Thus I think it's just a question of how much agita you’re willing to endure.