Driving with Roadguide in the province (Isabela) was often dangerous. Navigation led us through muddy tracks between rice fields and just 2 meter wide dangerous dirt roads. There was no differentiation between car roads or paths which can only be used by motorbikes or small 1.5 m wide vehicles used for agriculture. Navigation led us away from the main road following these paths just to save some distance but adding hours for the trip. There was no difference in route calculation whether we switched our Nuvi from the shortest to the quickest option.
In the populated areas like Manila or Angeles navigation Roadguide helps a lot, but in the Province you have to use an additional map to avoid ridiculous suggestions.