Guineafowl forage by walking steadily through vegetation, pecking at whatever they disturb. Their diet is broad: seeds, tubers, leaves, spiders, insects and, yes, ticks. Because they cover ground in flocks and are noisy, they are also kept as sentinel birds that alarm at snakes and intruders.
The tick reputation runs ahead of the data. Experimental work on guineafowl for tick suppression has produced mixed and modest results, with reductions that depend on tick species, habitat structure and how much of the property the birds actually use. Guineafowl prefer open ground and short cover, while the ticks of most concern often sit in longer vegetation the birds work through less.
What is well established is that they are dietary generalists that also take crop pests and, when kept in numbers, garden plants. Their value as an alarm system is easier to observe than their value as pest control.