I did very little guessing on the regular puzzle, which took me a little over 6 minutes, but the master-level one did require some brute force at first and took me much longer to finish. Once I got rolling, though, I was able to solve it intuitively. It's more like a sudoku but instead of mathematic logic you rely on your knowledge of English vocabulary and spelling. It may not have traditional clues but by giving you the pool of letters for all words it gets progressively easier as you fill in the grid and eliminates certain possibilities out of hand.

The only real issue is getting your initial foothold, especially if the grid's pre-filled letters are mostly common and not helpful in placement. Having a pre-filled J is much more useful than, say, a prefilled E.