I have the Brother P-Touch Cube Plus PT-P710BT (Amazon link).
When using the Windows-based P-touch Editor, you may have problems printing out Unicode symbols. This is caused by the program not having any fallback font mechanism. The unfortunate solution is to use this website's "Fonts that support" feature, and then search the app's font drop-down to find an acceptable font.
If there are streaks when printing, there could be two problems: either 1) the cartridge needs to be turned a bit, like when it was first opened, or 2) you need to clean the print head.
To clean the print head, get a Q-tip and some rubbing alcohol. This is the area that you're trying to clean. To avoid dropping any full drops of alcohol inside the machine, I usually "flick the Q-tip mostly dry" just before I touch the print head.
The manual has two important sections that mention different ways of printing with other applications:
Some benefits of being able to print from Inkscape: