My wife & I both have Agattu's, which we regularly ride off road. I found that the standard tyres just didn't work well particularly going uphill (especially when wet and slightly muddy). More than once the front end has drifted out resulting in me coming off and I also found the back wheel frequently spinning uphill.
As a result, I fitted these . . . Schwalbe - Marathon Plus ATB . . . the same old Marathon Plus (including SmartGuard), but with a more suitable All Terrain tread. I also fitted Schwalbe Inner Tubes with 40mm schraeder Valves at the same time.
Pretty simple to fit, although you do need to make sure the tyre bead is well seated . . . and I had to use tyre levers for the last few inches.
Handling seems to be absolutely fine and off road is much improved.