Grundlach has proven, since 1993 when he founded the TCW Total Return bond fund, that he knows how to find bargains in the mortgage market and produce superior returns.
The only concerns I have are that most of the holdings are CMOs rather than pass throughs, and pass throughs are usually less risky. Also, the fund has most all of it's holdings in the mortgage market, meaning less diversification.
Even the best fund managers can stumble, as Bruce Berkowitz did with his Fairholm equity fund after being one of the equity funds' best managers for years. Grundlach isn't immune to making similar mistakes, so while I think this is one of the best bond funds out there you can't just invest without monitoring it for negative trends.
I have 90% of my IRA in DBLTX and have counterbalanced it with 10% in SPY and GOOG. I agree that DBLTX should be watched carefuly keeping in mind the old shiboleth, "rule 1: Don't lose money and rule 2: Remember rule 1".