These will challenge you more than any dumbbell row. You'll be essentially rowing your bodyweight with one arm.
Don't let your shoulder shrug up, keep your core braced, and pull with control. You'll feel your core work double-time to stabilize the offset load. Your pulling muscles will also contract deeply. To make it easier, simply go flat footed or adjust your angle.
The boneheads in your gym only know one way to make an exercise tougher – add more weight. That's why boneheads never build more muscle, no matter how long they work out. Our resident Scotsman knows some remedies.