Power Towers are ideal when you are short on space, have a strong focus on abs or need an affordable option.
However…
Power racks are usually stronger, more steady and are designed for lifting heavy weights, as well as doing pull ups.
Normally racks do not have a dip or push up station, as they are lifting-centric, so to speak.
Power towers focus on using your body weight in place of weights, so it’s not an apples to apples comparison.