Which is best? Landscape or Portrait?

Viewing Offences and other Definitive Guidelines in Portrait is probably easier because the whole page is displayed without having to scroll around. You might still need to Zoom-in for the detail of the Offence, but you can still see where to Zoom-in without needing move the page around.

Looking at the same Offence in Landscape, you can only see the top of the screen and will have to scroll down to see Offence seriousness details.

Your Sentencing Guidelines App can be used in either Landscape (longest-edge nearest you) or Portrait (shortest-edge nearest you). Unless you have rotation locked within your tablet's settings, when you move your tablet between these two different orientations most Apps will adapt to the current display orientation. If your App doesn't change when you rotate between orientations you need to have look within your tablet settings for Settings > Display > Auto-rotate Screen or something similar depending upon your type of tablet.

When used in Landscape orientation most of the menus are immediately available. The judicial indexes are displayed down the left-hand side of the App. Clicking each index will display their content on the right hand side of the App. Depending upon your tablet size, you might have to click the three dots (circled in red) to access other tools. The App can be used without needing to use the tablet navigation keys highlighted in the bottom edge of the screen labelled Back, Home and Recent Apps.

However when using the App in Portrait, the Back button highlighted below is used to navigate back to the menu of judicial indexes. Therefore pressing the Back button on the screen shown on the left, returns the App to the Main menu of judicial indexes shown right below. Clicking the highlighted three dots button expands the menu of other Tools. Notice that when used in Portrait there are less Tools immediately available and more hiding under the "more" button.

However, the best resolution for using some of the Tools is in Portrait whereby the Tool is displayed at the top of the screen with the keyboard showing at the bottom.

For more information about Lock Rotation: the following is an Apple support article which explains how the switch can be configured: https://support.apple.com/en-gb/HT204171