Isn't it also overkill?

Given the claimed upper bound of 500 records (which means be generous and assume an upper bound of 1,000), it's still going to take fewer reads (and fewer disk head movements) to suck in an entire flat file of search criteria than it would to search using multiple DBM files.

There's a point at which the multiple DBM approach is a win, but I suspect this application is far below that point.